Am I a bad person?

So one of my sisters are pregnant. And I'm happy for her but I kinda don't want her to have another baby. See I'm the youngest of ten (I'm 19) while all my other sibling are all 29 and above. So being the youngest I live with my parents tile I finish college and get on my feet. But this one sis in particular, is married and has moved out and already has 2 kids. But. Those 2 kids live here and she basically leaves my mother to take care of them. However, both my parents are retired and get sick from time to time and then the responsibility falls on me from time to time and when I work I usually end up having to buy groceries and pays bills and stuff just to make things easier on my parents. With this in mind. I already know this third child is going to be another thing for my parents to deal with and I just don't want to have to take care of it. I mean I know it's my sis and I should want this for here and a part of me does but I hate that everyone expects me to help out just because I have no responsibility  of my own (Bear in mind that she isn't the only sis that does this)