Can I handle it?

So I took great offense to my sister wanting to put her kids in day care. I pretty much forced her to move up here from Idaho so that I could help her with the kids since she got divorced, but now I'm not able to care for them so what do I do now? And she doesn't need my counsel or advise or anything because she gets all that from our aunt, so what am I doing here? I tried to not take offense and at first I was okay with it but then it was like a shot in the back, because I think she'd been planning this for a while be hind my back with my aunt. Because now all of a sudden my aunt is watching her boy all the time because "we're making it easy on you" like I'm having a nervous breakdown and should only be allowed to harm my own child. Like I would harm her child. I'm a little worried that he might harm me, he's tiny and could trip me at any moment. So yesterday after the boy spent the day with the aunt my sister asks if I can watch her boy while she goes to class and I say "I don't know, do you think I can handle it?" and she tells me to shut up. She's the one questioning me! All I really want to do this afternoon is take a nap with my boy but I'm forced to stay upstairs and get harrassed by a four year old who thinks he owns the world. "Get me this! I want that!" and I want to say "F" off little boy! but I don't. Just because his mom lets him do whatever he wants he expects it from me and apparently has been told that its okay to not listen to me because I'm wrong and he's right.
So I came to the conclusion yesterday that they're doing all this to "help me" when really its just hurting my feelings, but I'll give in and let them "help me" and I'll do what I want, which is coach basketball and stay away from her kids. How terrible am I? I'm a horrid person.