how does a dad prove the best interest of the kids is for them to live with him
just a matter of neglect & spend no time with them not allowed in xtra carriculr activities cause mom wont run
13 yr old is failing school i belive its cause of home life

Well talk to an attorney, put together a case and seek modification of custody and explain that your kid's grades are bad and should not be, and you want an opportunity to change that around. I suggest providing the court with a plan that you can implement to improve things for your child.