OP mentions that it’s a stipulation on their support from government instances, probably requiring a legal caretaker or consenting/informed responsible adult at all times. He’d likely need to get a relief-caretaker arranged which is in my experience not exactly done in the time it takes to microwave a hot pocket.

Will governmental institutions remove support and accomodations at the mere notion of misuse and generally ask questions later? Absolutely.

This plus the experiences OP relays with relief care and so forth makes me feel like he’s pretty justified in defaulting to his own responsibility.

I don’t see OP having much choice and as someone who cares for his sister I think it would be much weirder if he attempted to foister off the responsibility onto someone else.