Florida family law, change in custody by non-custodial parent, parental neglect

Change of custody: My wife divorced from her husband about 4 years ago. When she left him, she left with the kids in tow. The oldest child wanted to see his dad so she allowed the dad to pick up the kids before any divorce or custody arrangement was made. The dad then kept the kids from her for about 5 months. In Florida you must attend a mediation before a judge will hear a divorce case so when she went to that mediation she signed allowing him to have custody thinking that he would be an adult about things and let her see them more than the guideline visitation. In the end, he has hired her mother to be nanny for the children. He works as a fire fighter 24 on 48 off. He does not abide by the agreement regarding keeping her advised as to Doctor appointments, preshool registration, school events, a surgery that one child was scheduled for, and multiple other issues. He allows no telephonic communication. We will not communicate with her at all. There have been multiple times where he has taken off of work to thwart her visitation because of his interpretation of the papers and just disappears with the kids.

She had a lawyer that advised her to document everything anf give it time. He suggested to file contempt evertime the dad would do something wrong to build a case, and then to file for a change in custody. The thing is, the lawyer only filed contempt one time after being asked to many times and never had the motion for contempt heard. Honestly the father is about nothing more than the child support money he receives. He doesn't take care of these children at all. When you speak to the kids they always speak of their Nana doing everything for them. does she stand a chance with these circumstances to have a judge change custody? What is the best course of action? With the major child suport payment that is being paid out we can't afford another lawyer to handle this matter.