In a 50/50 custody when can children change schools?

we have 50/50 custody (legal and physical), however rite after we split she moved out and took kids to a town 20 minutes away and enrolled them in school there before we filed for divorce. I protested however since then they still attend that school. kids were in school 1.5 years in my area. Now Kids have been going to school in her area for 2.5 yrs. She doesn't attend all school events, seems like 40% of events and only helps marinally with their homework when they are with her. I consistently help them with their homework every time. I most events 95% even though school is farther away from me. The mother doesn't spend much time with kids, since she is going to school evenings, also has a new baby with her new husband. She also has her mom who is helping with her new baby drop off and pick up kids. Also the mothers home is to small and kids have to share their room with grandma. How is it possible to change this situation so that kids go to school in my area (back to original school), since it is a better district and allow me to be better involved in their school? Or will this remain until they are 18? I have every wish to improve their lives and looking. I live alone when they are not with me and have a large room that is theirs (masterbed). Also planning to buy a three bedroom so everyone has their own room. Thanks for any comments.