Jcxx Here's my 2 cents worth. 
It sounds as if this elderly guy, who hasn't cared about anyone but himself for 21 years, now wants someone to take care of him - and you're the next on on the list after auntie and Mam, neither of whom, quite justifiably wants anything to do with him.
There may be shared DNA but this man isn't your father and has chosen not to be your father until he's in dire straights.
If I were in your shoes I would not be swayed by sob stories from him or anyone else.
Mam has the right idea, he's the past and hasn't earned your respect, your care or your attention.
He's just a selfish, narcissistic old man and they never change. He's absolutely NOT your responsibility. Don't be sucked in.