What your’re talking about used to be called “custody” but now the issue is “timesharing”. (ie how much time the kids will spend with each parent)
The judge is going to decide timesharing based on the best interest of the kids. Witnesses can testify about a parties’ ability to care for the kids, and dedication and nurturing. But sometimes a party needs to have a witness tp show that the other party isn’t fit to care for the kids or spend appreciable time with them. Psychiatrists and Psychologists and other experts may need to talk to the kids and the parents to see what will be in the kids’s best interest, and report to the judge on that.