Stressed out

I'm currently going to school to be an elementary school teacher. I have a four year old step daughter who lives with me during the Summer and the weekends. Problem is my God kids also live with me one is two the other is the same age as her. I love them all with my heart but being around all them when they can't share or get along is starting to make me rethink kids. And That's what I've wanted for the longest time. Since I've been married. Idk what to do. Can someone please help me?