No. No. No. No. No!
If you want to help your family out, that's all well and wonderful, but do it on YOUR terms, not THEIRS. And address the way your sister "requested" this of you as well.
Personally, I can't say what I'd do. My idiot sisters, at this point in time, would never "request" something of me in such a blatantly rude manner because I would literally kill them and bury them under my floorboards.... or maybe just curse them out. Whatever I'm in the mood for, lol