my mom specifically asked me to forgive my dad.

This is textbook victim defending their abuser, Stockholm Syndrome mentality. Everything you've posted about your father points to him being a complete piece of shit. "She deserves it for talking back to the officers," fuck that's so disgusting I feel like I could throw up.

Until he actively apologizes and explains why what he did was wrong in his own words, he needs to be cut out of his children's lives, just like he abandoned his wife. Stop defending this. Challenge him on what he says, every time. Show him it's not okay.

It doesn't matter how he used to be, don't defend him on the basis of that. What matters is what he's become, which is a piece of shit.