The first thing he should is get an experienced ATTORNEY!!!!
Let the attorney devise a plan for evidence
I would absolutely NOT have him play amateur sleuth and not have him make his own plan to gather evidence.
A good Christian family law attorney will know exactly how to proceed. Been there, done that. I ended up with joint custody and a Rock solid Decree. I went through a lengthy jury trial and my ex-wife had a very high profile scumbag atty (2nd of 3 law firms). I “lost” the jury trial but the Judge did much to overturn in the Decree.
It may get costly but it needs to be done.
See #58 above.
The father is intelligent and knows the family court system more than most people.
Attorneys are valuable but very limited in family court. Without evidence, the outcome is a roll of the dice. The outcome can boomerang.
Family court is a different creature than other venues of law.
All the homespun advice “Get a Lawyer” are ‘nice words’ only.
Of course, he knows when he needs a lawyer.
But he knows the system well enough to seek admissible evidence first, then talk to lawyers.