I need advice about a manipulative guardianship situation.

Location: Pennsylvania
I live in Pennsylvania and I’m involved in a guardianship/custody dispute involving my daughter. I believe the guardian has repeatedly made false statements to the court and has manipulated the process. I also have evidence that they may know the whereabouts of someone who is a fugitive, although I don’t know if that’s legally relevant.
My legal questions are:
If I have evidence that a guardian has been dishonest outside of the guardianship case, is that relevant to the court’s determination of their credibility?
What type of evidence is generally admissible to show a pattern of dishonesty or manipulation?
If I believe someone has made false statements in court filings, what is the proper legal way to address that?
Does unrelated criminal conduct or knowingly assisting a fugitive have any impact on a guardianship or custody case if it affects the child’s welfare?
I’m not looking to retaliate against anyone. I want to understand what evidence a court would actually consider and what the proper legal process is.