I agree re meeting him first.
I would hope, in that meeting, to agree upon a consistent narrative about why dad has not been in Mo's life...something that is true but not too full of drama from dad...for instance that he wasn't ready to be a parent, didn't understand how to be one, that as he has grown and matured he has realised that he is an important part of Mo's background etc.
I'd also be wanting to get some idea of what his intentions are.....does he imagine regular contact with Mo, for instance/
That's likely somewhat inherently impractical, as these guys sometimes can't deal with the emotional impact of realising the magnitude of what they did.
I'd have a true, but making sure it is all about the dad, nothing to do with Mo. story ready for if dad says he'll do things thta he later reneges on.
Wow...this is big.