I'm starting to hate my sisters kids.

My sister just gave birth about 4 months ago to twin boys and I'm at the point of hating them. Since I was younger I've know that I would never have kids; I'm autistic and I've always thought I'd be a terrible mother bordering on abusive because I get super angry and annoyed when not left alone. My sister had childcare lined up for every day of the week except for Mondays so she asked me to babysit for her and she'd pay me. Ever since I have agreed to this I have been severely miserable. They cry all the time, they require so much attention and, they have so many body fluids releasing all the time. I know that these are normal baby things but i just simple don't want to be around it at all and i have to for 8 hours a day. It has gotten to the point where if they're both crying at the same time and I can't calm them down I just sit there and watch them yell for a couple minutes because I simply don't care enough to help them, or I'll yell out of frustration (not at them). I genuinely don't know what to do because including tomorrow I have 4 more weeks of babysitting for them and it's making me feel physically sick even thinking of having to be alone with them.