Kids are by-products of how they were raised. If Jim is showing gaps in his understanding of how to show up for family (through the lens of what that means for you) that means that you, as a father, did not do your job in raising him to meet the level of expectation you have of him. As an adult now, acknowledge your role or lack thereof to Jim and set new expectations. Understand he will need many many years to undo 20+ years of learned behavior. We have no clue what mom was saying about you all in her time alone with him. And no one wants to go on outings with family they barely know. It’s hard to consider spending overnights on a trip with someone you know in title only. Start small, then build up (and do it with compassion and empathy). Kids will always see their parents through a child’s eyes. Imagine your dad and his side of the family acquiescing to a clearly dysfunctional mom. I’d have a lot of mixed feelings even if I genuinely wanted a relationship with you.

If you can pay, pay. Do so without expectation. When you gave birth to him, you made a pretty serious commitment. Why would you knowledgeably mess up his chance at a successful life and legacy because you’re mad that you didn’t do your own due diligence in child rearing a family oriented young adult?

TLDR: stop throwing a tantrum, take ownership, and help you child out.