If you think about it ...

Presuming that a memory card has files on it in an appropriate format, if a computer cannot read the card in DOS then either the card reader or cable is possibly bad AND other WINDOW's based drag-and-drop options will be futile.

WOW!

Really?!?

Just what can your nephew NOT do with his current camera & lenses that he thinks that he wants to do which a different camera & lenses will allow him to do?

AFTER he figures that out, then he can add the appropriate accessory/-ies ...

FWIW. My opinion is that ANY-and-ALL future lenses should probably be Nikon/-compatible since future compatibility (with-or-without an adapter if he switches to Nikon OR sticks with Canon OR changes to a different camera body brand) is assured vs. buying a Canon-compatible lens.

BTW. It sounds as though BOTH your nephew & his instructor have G.A.S.

This is after-the-fact since you have managed to transfer the images ....

BUT, while it may seem tedious at first, if YOU/anyone know(s)/remember(s) how to use DOS Commands, then you/(they) can simply execute a simple COPY command from one directory to another if the problem ever occurs again ...

Either individual files can be named & COPied or *.* can be used or variations of *.*.

Let me be ONE MORE person to note that you need to be less than half the distance from the subjects you are shooting ...

You mind's eye is not in synch with how you think the image might/should OR actually will look ...

And, closer to 1/8th the distance between you and the subject will possibly achieve the look you were hoping for.

IRFANVIEW (freeware) will open a Panasonic RW2 file and let you re-save it in any variety of formats from .ICO to .RAW and almost everything in between.

Do you really need a wideangle lens with autofocusing capabilities?!?

I can't speak to the 20mm Nikkor or the 21mm Zeiss lenses which you are thinking of, but why not just opt for a vintage 24mm f2.0 Nikkor AI lens (which I recall was supposed to be a superior lens when compared to its slower Nikkor f2.8 variant; and, which is probably the basis for the 24mm f1.8 lens you included as a possibility) which will cost you a fraction of what the latest iteration of the lens will cost?

Canon made a lot of SLRs in the early 70s ...

The F-1 was at the high end, but even that seems to be available for a comparatively modest amount of money, now.

AFAIK, if your friend plans to sell it, then at the moment he won't get a lot because it seems that the ONLY Canon film cameras & lenses which have retained any significant value are Canon's older, Leica-Thread-Mount lenses and compatible bodies.

Regardless of the model, if the camera body works and IF your friend actually USES the camera and/or only its lenses, then it will be worth a lot (to him) ...

FYI. There are only a few, AFAIK, 35mm film lens camera mounts which are not readily available for use on a digital camera body -- the German PRAKTINA and the Russian START cameras come to mind as 35mm cameras which have lens mounts for which there probably isn't an off-the-shelf lens adapter.

Canon FD and the older FL lenses share the same breech-lock mount ... a 1974 camera will probably have FD lenses ... adapters are readily available for the FL/FD-to-digital mount of almost every ilk ...

SOME limitations may exist due to the flange-to-focal-plane distance unless the digital camera body is of the mirrorless variety.

Oh, you are "Right" ...

BUT, all answers posted can-and-probably-should be considered to be both specific to the OP + others (e.g., lurkers et al.) ...

Hence, the wordy preamble & post script where I suggested that the OP might want to simply consider a Leica ...

Regardless. to quote myself:

" ... whether today or some time in the future years to come, YOU (the OP, of course) really need to ask what you expect the next camera body (regardless of who makes it) will provide you that your current camera body & lenses can't. "

I think that s/he (the OP) + many of us (probably!?!) need to consider why we buy the equipment that we buy.

BTW. Admittedly, not all of my purchases can be considered to be utilitarian; so, I'm not trying to suggest that people shouldn't buy this-or-that because it pleases them to do so; but (IMO), if the OP truly has a self-imposed limit on expenditure then s/he really ought to think about what s/he hopes to achieve with the purchase of a different camera body than the one which is currently being used and/or future purchases down the road.

If YOU are thinking about going to a camera with a Full Frame sensor, then now is the time to switch to Nikon ...

If you are considering going to a FF camera (and if Sony is not a consideration) then while I love Canon, I have to ask "Why cripple your bank account with Canon's never ending lens mounts?" because if-past-is-prologue then Canon is bound to introduce another lens mount which may-or-may-not-be-compatible* with their existing camera bodies before you stop taking pictures.

* An adapter which will allow the 'old(er)' FF Canon lenses to focus to infinity may-or-may not become available, and vice versa, on Canon's next lens mount.

If you are just looking for another camera body to dabble with as an alternative to your Canon, then you may want to consider an m4/3 body.

IMO, whether today or some time in the future years to come, YOU really need to ask what you expect the next camera body (regardless of who makes it) will provide you that your current camera body & lenses can't.

BTW. IF you've got money-burning-a-hole in some really deep pockets then consider buying a Leica + some Leica lenses.

It is melted down ...

I believe that in the past that the few lenses which might have external blemishes on the barrel were sold in Japan in a "factory" store.

IMO, as a person who took pictures of various sports + other subjects for my college newspaper for several years, I will tell you that 'good' Sports photography at any level beyond pics of your kids or grandchildren at their games demands that the photographer know the sport AND THEN (as donolea & tomcat suggested) the photographer benefits from knowing what shots worked for others (or, themselves) in the past AND THEN it is often beneficial to know the players (on BOTH the home team and the visiting team) who may be more important if the pics are to accompany a news story vs. a pic for your portfolio because a great pic of a player with a sub-.250 average who strikes out 4x in a particular game won't mean too much for an editor if the pic is for an upcoming paper or other publication.

In addition to assessing your own knowledge-and-skill level, you need to know limitations of your specific camera equipment ...

As donolea also inferred-and-suggested, you need to know what lens will work in which lighting situation. A fast lens is almost always better for Sports photography ...

And so, you need to know your lens(es) and their capabilities-and/or-limitations unless you are taking 'static ' shots. Most of the moments are very transient in sports and you often won't get a second chance -- you do NOT want to be futzing with the zoom's range when you should already have been focusing on the action on the field.

ALSO, I think that YOU will need to figure out if your camera's auto-focus will be an impediment OR if you need to manually pre-focus your lens on a specific player-and/or-spot on the field.

In the end, the better prepared you are the more likely you are to make-your-own-luck with regard to getting shots which will be of interest.

A tripod-or-monopod may be beneficial.

BTW/FYI. Back in the day, before indoor arenas had TV lights, the Sports Illustrated photographer would set up his own lights the day before a game. In other words, a lot of preparation was made with zero assurance of a usable "Sports" picture from a particular game.

In addition to the use of a tripod, YOU need to decide how much of the branches you want to be silhouetted ... (AND, how well) ...

In other words, if you want the branches to stand out more then you will probably want to be more aware of the balance of twilight with the street light ...

A multiple exposure may be beneficial IF you also want any detail in the surface of the tree trunks; so, a tripod would absolutely be required ...

FYI. A million years ago, when I wanted to take a nighttime cityscape from a highway overpass which included details of the buildings sans cars ... at dusk, I exposed the film (relatively slow ASA -- i.e., Panatomic) at HALF of what I normally would have exposed the film at and then the remainder of the exposure was my best guess at the long exposure to complete the image. The result was a "night" shot which had the clarity in the buildings which I was hoping to achieve.

If detail in the surface of the tree trunks is not a factor, then a single exposure will probably suffice; but, the timing will make a difference ...

YOU will possibly need some trial-and-error to work out the lighting balance you want.

BTW. Using your current Canon lens(es) on the Sony A7 body (or, any other camera body) will probably allow you to better assess whether the advantage (e.g., low light use, weight, etc.) is a greater benefit than optical viewing, etc.

FWIW. My vote is for an adapter since he presumably has a very good lens on his Canon -- that is, unless the OP has the deep pockets which many UHHs apparently have, I think he should try his current lens(es) with an adapter bought via eBay directly from China-or-wherever (Why pay more?), first ... he should just try to buy one with the better-or-best rating based on feedback (also, check Amazon for sometimes-real/sometimes-fake reviews) ...

The OP can always buy MORE lenses at a later date!

AFAIK, the Canon M5 (¿probably?) has a version of the smaller APS-C sensor vs. the SONY A7's "full frame" sensor.