jim quist Loc: Missouri

If you want natural smiles have them do a loud fake laugh. At the end of it will come natural looking smiles and the real laugh.
Since there is no background to throw out of focus and they won't all be on the same focal plane, use an f-stop around f11 or so to get it all in focus

Grand Loc: Lebanon, Pa

85 1/2 or 1/8.

GoofyNewfie Loc: Kansas City

Explain the “1/2 or 1/8”

gvarner Loc: Central Oregon Coast

Excellent advice. And be careful about the light. Some simple on-camera fill flash could be very helpful if there’s harsh light. If you’re within 10' the ol' pop up will do, otherwise use a Speedlight. Shoot a few with and without.

camerapapi Loc: Miami, Fl.

Lots of advise here, perhaps confusing for you. Understand that we do not know how you plan to do this, if shooting individual portraits or groups. Understand there are head and shoulder portraits and 3/4 posing although the whole figure is also a portrait. Each application deserves a different prime or a zoom depending on the subjects. I do not know what you intend to do with your models so I will offer general ideas.

The late Monte Zucker used the 18-135 for many of his professional portraits. Between 35 and 100 mm. the lens should do very well. The 50 mm lens has a very useful focal length and it could fill the bill for many shots. The 100 mm lens is very useful for head and shoulder portraits. If you know how to use flash keep in mind that its light can soften shadows and reduce contrast. For groups depth of field plays an important role and I will advise you to focus 1/3 into the group using an aperture of around f11. Always be aware of the direction of the light and do not let it to shine on front lighted subjects. It is far better to place the subject or subjects with their back to the light and fill the shadows with flash.

I know all this could be complicated for a person who is not into portraits. Posing the subject is important if you want natural looking portraits.
Finally, a tripod has already been suggested and I will use one if I were you. Good luck with the shooting.

Blurryeyed Loc: NC Mountains.

I agree with what LWW said, the 50mm is a good portrait length for a T4i and because of the wide aperture it is capable of producing the creamy backgrounds that we associate with portrait photography. When shooting families I would suggest that you be careful in shooting wide open with the lens because the depth of field can become too thin to keep all the people in proper focus. I would also carry the 18-135 along just incase you find yourself in a situation where the 50mm will not frame the entire family, ie porch is too small for you to properly frame the image you want.

xt2 Loc: British Columbia, Canada

Or maybe, just maybe, take a few shots with whatever lens is your favourite and use a touch of fill flash from your camera and forget about making the whole affair such a scientific exercise?

Stay safe & healthy...

E.L.. Shapiro Loc: Ottawa, Ontario Canada

KISS!!! An acronym for Keep It Simple Smart person! Travel light and travel smart. That 17- 85 should cover any "portrait" situation.

Most portraiture is best done with slightly longer than normal lenses and what with social distancing, that's a good duel purpose. Individual close-up and 3/4 length portraits will work out well at 85mm, full length and groups- go to 50mm. Stay away fr wide-angle focal lengths unless you are cramped for space and have a very large group.

Aperture settings- If you are familiar with the depth of field control you have the option of rendering the background IN or OUT of focus.

Lighting- If the light is diffused and even, you are good to go. If it is harsh and there are dark distracting shadows, employ your Speedlight as a fill light source.

Posing- 24 hours is too short a time for precise posing lessons. Keep it simple and fun. The concept of "Porch Portraits" during pandemic isolation is to provide therapeutically beneficial fun and a good time in the midst of a bad time. People should hug (not the photographer) relate to each other, shoot some folks doing activities and also looking at the camera. Smile will emerge with friendly conversation. Shoot a bunch and put them online and let folks choose.

So TODAY- go out in front of your own house and line up your cellmates and practice. Nobody is gonna expect masterpieces- great expressions and fun will carry the day. You might call each family and ask them to coordinate their clothing- whatever, genes and T-Shirts, dressy, silly. Give them something to do that will help pass the isolation time and garner interest.

If you are good and steady in handholding your gear, you probably won't need a tripod. It will be easier for you to travel and quickly shoot from different angles. At ISO 200 to 400 you should be good to go with manageable aperture and shutter speeds.

Do not bog yourself down with too much gear- concentrate on those expressions. I'm telling you this form 50 + years of portrait and event coverage experience.

Thanks for helping charities and giving folks something nice and fun- very important theses days!

Good luck, be well, stay safe and STAY well! Oh- post some of your shots!

frankraney Loc: Clovis, Ca.

You've already been given a good suggestions by Alan and others. I'll just add what made him great that I would get hyperfocal pro for your phone enter your camera and lens combination and and you'll be able to see your depth of field. For instance with a 50 mm and 15 ft away, you will have about 2.8 ft in focus half of that in front and half of it in the rear. At f2, that drops to to feet. At 90 mm that distance is cut in half so you'll need to back up to 20 feet. Hopefully the porch is long enough you can do that and stay at the same level as your subject and keep everyone in the shade. Anyway sounds like fun wish you the best, shoot away.

CHG_CANON Loc: the Windy City

Neighborhood porch portraits are not studio head shots. Your 18-135 will be useful, and your 100-400L will probably be even more useful, given the expected shooting distances and group sizes. The 100-400 drawback is the size and weight, if that is a consideration for this project.

Alafoto Loc: Montgomery, AL

Agree 100%

MichaelMcGrath Loc: Ireland

Of what you have, Marg, I'd fancy and use the 100L. Best of luck with your worthy project.

MichaelMcGrath Loc: Ireland

That would be on my Canon 1Ds mark 111, of course, brilliant pro camera for portraiture available at reasonable prices now.

Retrobug

One thought not related to technique: ypu propose “quarantine” porch portraits, so you are photographing a moment of history as well as documenting a family? Consider giving each family 2 photos: one portrait showing faces, and a second with same composition and masks. That tells the story of the quarantine and might provide a historic documentary value to great grandchildren beyond the usual family value. Just a thought. Feel free to take it or leave it.

tgreenhaw

If it were me I'd put the 18-135 on the T4i and the 100-400 on the 80d. I'd consider putting the heavier setup on a tripod for posing with the lighter slung over the shoulder for candids. Depending on the lighting situation, you may want to use fill remote flash if you have It. Also review a DOF chart for expected exposure settings to be sure focus is sharp on all eyes with the proper aperture.

It's a bit hard to say for sure though because I don't know the size of the group or rough distance you will be shooting.

Bring the 100 too because if you don't need the flexibility of the 18-135 or 100-400, that would likely be much sharper and allow for a shallower DOF