No sympathy for the son for being kicked out. He's an adult and self-sufficient, the grandkid isn't.

I can't say I have sympathy for the son being kicked out, but I do have sympathy for him given that his father is choosing his granddaughter over him. Also, I think it's important to point out that we have no reason to believe the child's mother is in need of financial help from OP's dad, so it's not like OP's dad needed to free up resources for the grandkid. He just chose to do so because he wanted to, which is his choice, but that doesn't make it a necessity.

This went on for a while when I told him that if he didn’t think his own child deserved a father then he didn’t deserve a father himself

That's unnecessarily harsh and a really gross parenting move IMO. Hopefully now that OP's had some time to reflect, he realizes that he could have asked his son to move out without essentially disowning him. Not even essentially, actually:

I chose to end my relationship with my son

I definitely have sympathy for the son for that.