How do I tell my sister that her children will not be welcome in my home daycare once I get it going?

My hubby and I are buying a house with a huge inlaw apt. Instead of renting out the apt and getting a maximum of 700 a month, I am going to use the apt for a home daycare so the kids won't be in our half of the building at all. The apt has a bathroom, living room, dining room, kitchen, and one large bedroom, and the state/ town will let us have up to 5 kids there full time. We are going to start with 3 full timers. I want to offer the apt to my younger sister (20) free with no rent, provided she can help me with 2 additional kids 2 days a week. Then she is free to work her regular job 5 days a week (she works part time). This way, she will learn some independance and feel like she has her own place and I can get some help with something I've never done.
My older sister (30) is going to be pissed about my offering our little sister the apt. She is currently living rent free with our parents and not even paying for the utilities she is using, which is puting some severe financial strain on our parents. It is just her personality that if anyone gets offerred help, she expects it to be her, since she has just divorced and has 3 kids.
Her kids are also WAY out of control, and her middle child is severely autistic. I am not equipped to handle her kids, and I don't want to, and I shouldn't have to. I know my sister will try to get me to "watch" her kids free "since I'm watching other kids anyway". I don't feel she deserves any more handouts from anyone, and I'm not going to lose my sanity helping her out. She was given (yes, GIVEN) a FREE house all paid for and 2 brand new cars all paid for by his family when they got married. Since the divorce, she has lived free with our parents and has been getting ssi for her daughter, food stamps, and child support for the kids. That to me is enough. She isn't getting anything from me.

I know it sounds heartless, but my hubby and I are both from poor families and have had to work for every single thing we have. We have 2 kids and are hoping to use this house as a stepping stone to get the farm of our dreams. We are very smart and good savers. We have been married for 2 years now and have only ordered takeout 4 times in that time. We buy all our clothes second hand and most of our food at the discount store. That amount of saving has gotten us this house, and we want to pay it mostly off, sell, and have money for our dream home. My older sister does nothing but complain about everything, and my younger sister deserves to have a try at living on her own. WE want to give the chance to my younger sister, and that is our choice.