Is what the questioner did, concealing his mother's betrayal of his father out of fear of the family's dispersion, the right thing, or should he have confronted his father, or what should he do to please Allah?

Concealing what you saw is the correct thing to do, and you must cover your mother's fault, for the Prophet, peace and blessings be upon him, said: "Whoever conceals [the fault of] his Muslim brother in this world, Allah will conceal his fault on the Day of Resurrection." You should advise her gently and kindly and prevent her from committing sins. This is not an act of disobedience but rather a form of righteousness and benevolence towards her.