Well, I don't really have any general wedding suggestions, and surely nothing that compares to the others' postings, buttt, here's a fun (albeit renty/equipment-needy) idea..
DISCLAIMER: the practicality of this is highly-dependant on your (your brother's and his wife-to-be's) family and friends, I imagine. : D But if you're shooting their wedding, it sounds like they are more of the casual type, and may enjoy it.
I was at a wedding, once, where the photographers had set up a bit of a mini photo studio/booth where guests could go over and take their own small-group photos during the reception. I believe for part of it, this was actually a manned station (there were at least 3 photographers at the wedding) for the important family photos, where they'd take care of organizing/posing them and taking the shot. However, for the rest of the reception, we could just go over with friends and snap our own pictures. It was actually a whoooole lot of fun (for a few minutes, at least... and that adds up among different groups of guests!).
Though they wouldn't exactly be WEDDING shots, you would have some nice, consistent (very controlled lighting - minimal processing) family/friend portraits that could range from lovely-shots-with-the-grandparents-and-grand-children (for non-wedding use, etc..) to friends-drinking-one-too-many-and-rolling-around-laughing-and-taking-pictures-of-themselves.
It's pretty much a possibly useful or possibly pointless set up, depending on the wedding style.. : D Again it depends on what your brother and his wife-to-be want for memories and/or to share with family and friends.. like "Hey! Here's that picture you guys took of yourselves! It came out great! Enjoy it!" OR "HAH, we're keeping this one for blackmail down the road.."
Anyway, you pretty much would have zero processing on those pictures (maybe a batch lens-correction / barrel distortion), since you'd set up proper exposure before hand, so however many pictures were taken, all you'd really need to do was sort through for the good ones.. (I imagine if you gave them all straight-up to your brother and his wife, then they might get overwhelmed if they have a thousand family/friend portraits to go through, eventually making them quite sick of the things!) But I digress..
Here is what you'd need for the set up (unfortunately it's a bunch of stuff..):
1) a low traffic area at the reception (a corner..) - probably don't want it TOO far out of the way, because you want people to be near it, but you also don't want them to drunkenly (or dancingly) crash into it by accident, either.. Near a (neutral colored) wall will also give you some extra fill-light from the flash bouncing off the wall (see below.. essentially flash from a bounce umbrella will be coming at them from a bit of an angle opposite a wall... that light bouncing off the wall should lighten the shadow side and help even out the lighting).
2) dedicated camera - this could be your backup DSLR (a 3rd one besides your t3i and your wife's 60D), OR it could be a smaller camera like a Canon G12, etc, that has a hot-shoe.. you really shouldn't need anything amazing for the camera.. ** unfortunately you'd need to ponder number 5 below (shutter release cable) **
3) a wide-angle lens - nothing fancy.. the 18-55 kit lens should do just fine at 18mm (you'll want to do a batch barrel-distortion correction in post-processing, though). I think the G12, at its widest, has about the same focal length. The focal length is some what of a compromise.. a longer focal length will give you less distorted family members, but you're going to have a significantly larger "photo booth". (PS someone chime about where to put the thinner/thicker people..? thinner people at the edges in this sort of mid-close range shot...?) However, if it's more of a fun/casual thing, I guess a little distortion isn't the end of the world.
4) a tripod for the camera - perhaps attach a weight to the tripod, to keep it from getting moved too much and/or knocked over.
5) shutter release cable / remote switch would be recommended - this way, you'll keep people away from touching the camera.. unfortunately, I don't know what non-DSLRs accept these..
6) flash - I imagine any flash will do, since this will be used in a very close setting, as long as it works with a hot shoe cord and/or isn't really old with high-voltage that can fry your hot-shoe. It *will* need an adjustable head.
7) flash umbrella - increasing the size of your flash..
tripod / flash stand for the umbrella - you'll want that light a bit off camera, to the side, perhaps..
9) hot-shoe flash cord - this isn't really required.. You can mount the flash right to the top of the camera, and point the flash toward the umbrella that's to the side of the camera.
10) a chair or two, and some sort of simple back drop (a plain wall, if in the corner..?)
11) flash card(s) / extra batteries!
I know it's a lot of stuff, but depending what kind of spare camera/flash you have and if you already happen to have a tripod and a flash umbrella, it could be a fun (and easy) thing to set up.. : D
Maybe you'd have to worry about people knocking it over, or manning it at some point.. Technicalities, technicalities.. : D Perhaps find your most-trusted child or niece/nephew and give them 20$ to be a photo-shooting rock star for 30 minutes, etc.. maybe 2 of them, so they keep themselves entertained. You probably know the limitations of your family. : D
Anyway, sorry for the longness factor.. Again....
DISCLAIMER: It was fun to use as a guest, though I seriously have no idea how useful the pictures were to the bride and groom. They thought they were fun, but they were definitely NOT "wedding" pictures.. more of an added-bonus.. So definitely don't spend too much time on it.. I think the whole point is being able to set it up (if you have the gear), and then let it take care of itself.. Then come back later, and you have a whole set of pictures! : D
Also, I know I didn't really explain the exact set up, so if you don't get it, I can easily draw a picture and post how you would set it up. : D