One thing to keep in mind is the R10 has a APS-C size sensor. That means that the effective focal length of those lenses will be higher than on a full frame camera. I believe Canon uses a 1.6 crop factor for their APS sensors. So, while a 24mm lens is very wide-angle on a full frame camera, it will be only moderately wide on your camera.
For portraits, a moderately long lens usually produces more pleasing results than wide angle. Wide angle lets you capture more of the scene around a person, but then it's more of a landscape that includes people, not a portrait. A portrait should focus on just one (maybe two) subjects.
Of the lenses you mentioned, the 15-35 is probably your best bet. It's a "L" lens, which is Canon's top-of-the-line. It's fairly bright.
You might also look for Canon's 50mm f 1.2 or f 1.4 "L" lenses. With the crop factor, 50mm is comparable to 80mm on a full frame.
Your subjects will fill the field of view. You might have to take a step or two back, but they'll look better than when shot with a wide angle lens close up.
Thanks, I feel like this a lot. I love taking pictures with my “cheap” 50mm, and if I didn’t restrict myself to one lens only I’d bring that too because I just love it.
The 15-35 is the one tempting me the most, I’m just asking knowledgeable people if it will be enough for me with my crappy hands given the low light environment :)
Do you already have the 50mm f1.8? That's a good portrait lens. Not as sharp or as bright as the much bigger, much more expensive "L" 50s, but still brighter than a f2.8 lens.
If you've got the 50mm, my advice is to take that to the party as your only lens. If you're going to spend money on something, spend it on a flash.
With a flash, you should be able to stop down, even at night. Try f/4 or f/8. That will boost sharpness. If you're concerned about weight, consider the Canon EL-100. It weighs 6.7oz without batteries. I'm guessing it takes either 2 or 4 AA batteries.