As noted above, you can still use LR to export your edited images to jpg (or other available formats). For most family use, high quality jpg formats are ideal since they are widely used and people are familiar with them. Although the jpg is less than 3 decades old, it has emerged as an important format for image storage and display and is supported by all current operating systems. Given the wide use of jpg formats, I would guess that images in that format would be readable for the next 50 years or more by consumer devices.
The file name is in the metadata panel. I am not sure whether or not you can edit the file name or other metadata in LR after stopping the subscription, but you can certainly change file names in the OS outside of LR. As long as you have a current subscription you should:
(1) copy your catalog file with a new name.
(2) Open the new catalog and do your aggressive culling. That will give you your original catalog with everything and a new catalog with only the images worth handing down. The advantage of culling in a separate catalog is that if you screw up, you haven't lost anything. All your originals are in your old master catalog.
(3) Unless you already have meaningful file names, rename all the images so that the image file name will tell the observer what the image is about. Probably easier to do in LR than it would be to do after the fact using the OS.
(4) Export everything in the new catalog. All the keywords are preserved in the exported files in the metadata. I don't have a Mac, but Windows File Explorer will let you see the keywords. Right click on the file, click on properties. On the Details tab, the keywords will be listed under Tags. This may or may not be useful to your successors depending on just how familiar they are with the concept of metadata.
(5) Produce an organized folder structure to hold your image files and save the images into the appropriate folders.
(6) Copy the folder structure to a robust medium and distribute copies to all your relatives (or other heirs).
Meaningful file names should be part of your workflow so that you don't have to change things later.
The organized folder structure should be generated now, while you have all your faculties and can think about it coherently.
The only problem with this approach is that whenever you take a new photo you have to put it in your old master catalog and then consider whether you have to copy it to the new catalog for your heirs. In the new catalog File > Import from another catalog will allow you to copy images from your master catalog to the new catalog (including all the keywords and edits).
Alternatively you could skip items (1) - (2) and create a collection set in which you create topical collections. You can then place your worthy images in the appropriate collection. In that case you don't have to delete anything, just fail to add an inferior image into one of the collections. This approach may be more flexible, as you could add or subtract images from the collection later (i.e. continue your culling later). Items (3) - (6) above should still be done.
CHG_CANON suggests:
(A) 2048 pixel wide limits (or wider). Personally, I think they should be saved at the original width. They can be reduced by the heirs if needed. Harder to expand them if the heir wants to crop them.
(B) Paul gives a sample file name. I think the date is important. YYYYMMDD or YYYY-MM-DD is a good date format (ISO8601) and can be sorted numerically and chronologically the same.
(F) I am not a fan of CD/DVD as a storage medium. It is certainly a good transfer medium but when sharing with your heirs are they likely to transfer the files to a more robust medium? You want a medium that will last. Media change with time and a medium that is good today may be inferior tomorrow. Archiving data/images requires maintenance. I should point out that none of my digitized images is more than 35 years old. The longest lasting family photos I have are all prints (silver on paper).
Paul's other recommendations are good.
Further, consider generating annotated versions of important photos. This involves adding text to the image, which will alter any artistic quality in the image, but will be very useful to people looking at the image a century from now. In particular be sure that names of people in the image are included. In the metadata at a minimum, but for important images they should be in the annotation. I have a writeup on
Adding Documentation to Family Photos which might give you some ideas.
You have a lot of work to do.