What complaint or cases to be filed against a mother who left the sole reponsibility to the father? My sister-in-law was not visiting her two minor children for a year. NO financial support, morally, physically, caring.. none at all.. What do we do in this legal problem?

The courts handle financial support and verifiable abuse or negligence, and all the rest about love and caring is just between the parents. The father goes back to court and sues for past due monies, and possibly a change in custody/visitation as leverage if she ever decides she wants to be part of their lives.