Can I be held responsible if my sister leaves my dad with people we don’t know to care for him?

If she is getting paid by the state to care for him, then she should be caring for him. Yes, she needs a break, but then he people who take over should know the basics of the care he needs. You could take CPR training, and she should leave written instructions about medications, but she shouldn't be gone long if she is being paid. The state likely has rules about this so you may want to check into that.
Carol

There are respite care services. You just have to search online or call your community center about this. But I strongly agree with MindingOurElders, it wouldn't hurt if you train for CPR.

42:

Sounds like you care more about him than she does. That being the case, have a chat with her and let her know how leaving him with strangers who don't know their a__ from a hole in the wall affects you. Also, tell her you're interested in free trainings (I'm sure there's a few in your area) so you can both share the responsibility of caring for Dad. ... Who knows? You just might become his primary caregiver. Good luck.

-- ED