There are already a lot of good answers/opinions/experiences/etc. here and I don’t want to rehash all of that, but I will mention this:
If you’ve heard the expression, “blood is thicker than water,” you should know that the original unedited expression was actually, “the blood of the covenant is thicker than the water of the womb.” Basically meaning that the friendships (covenants) you make in life are stronger bonds than the family you just happened to be born into.
You can’t choose your biological family, but you can choose your friends and (non-bio) family. Don’t let people drag you down just because they’re related to you. Cut the dead weight out of your life, regardless of relation, and live your best life. If your dad doesn’t care about you, then why should you exhaust any energy caring about him? He hasn’t earned your attention, nor the attention of his grandkids.
My wife came from a poor trailer trash family and felt obligated, as the only person who made something of herself, to attempt to support her grandparents (who raised her), mother, and 3 siblings. But it only led to greed, gluttony, and dishonesty. Eventually, she had to cut ties with most of them because they started to feel entitled in sharing her “wealth.”
We had to draw the line when one of her pregnant sisters was about to have her baby taken away by the state. (I believe it was her 4th one the state had taken from her at this point; she had been deemed an unfit parent, but kept pumping out kids regardless.) My wife’s family tried to guilt us into adopting the kid, just to keep him in the family. She finally put her foot down. Taking in illegitimate children from her family was just trapping her with the burden of her siblings (who were already trying to pawn off their kids to their grandmother). My wife cut ties and now only speaks to her siblings (and mother) if they call. But she makes zero effort to stay in touch otherwise, and she won’t give them anything except functional Christmas gifts - the one time of year she indirectly contacts them.
My wife had deep-seated anxiety for years, worrying about supporting her deadbeat family. Now she’s low-contact and made a rule not to support them financially. She’s living stress-free now and is in a much better place for it. Their lives are their own and she refuses to feel responsible for the horrible choices they’ve made.