To me it sounds like unconditional acquiescing, not unconditional love. "Dan" sounds like my own father, a classic narcissist. I was your "James," the mediator, for a long time, until I left home, left the toxic dynamic, & realized that I no longer needed to play into it.

In Dan's world, everything revolves around Dan, and if you should be so selfish as to make it not about Dan, Dan's struggle and what a martyr he is, and how wonderful & amazing Dan's efforts are, you're being the asshole.

If Dan does something to wrong you he will twist it around & make it your fault, gaslight you into questioning whether he even wronged you, & manipulate you into acquiescing to what he wants.

Dan has to be in control of the situation and all of those around him, which is what it sounds like he's doing by domineering the planning of this trip. He doesn't give a shit about if you have a beef with him, or repairing your relationship, as evidenced by the lack of contact the whole month. He only cares about having all those around him emotionally under his thumb.

The number one takeaway from all of this is that narcissists don't change. Dan is not going to change, not without some kind of traumatic or life changing intervention, which you are not capable of facilitating. It is not your job to fix Dan, or accept his behavior.

If I were you I would continue ignoring Dan. Refuse to engage or interact with him until you get an apology--which you have to accept you may never receive. To me it sounds like Dan is not going to apologize, so it is up to you to decide what you will do with that.

Are you going to let it lapse, acquiesce for the sake of family "harmony," and show Dan that: A) his behavior is acceptable, and, B) that he can push you around emotionally? Or will you choose to ignore him, disengage with him, minimize interaction when you are forced to be around him, and stop giving this asshole power over your life?

You can't dump your family, it's true. But you can minimize contact and distance yourself emotionally from these toxic sort of people. Dan is toxic. My father is toxic. I've dealt with my father by minimizing my contact with him to only pleasant / surface-level interactions. Once I decided to stand up for myself I spent years demanding apologies that I would never get from him. I realized it wasn't worth it, have pushed him away to arms length, and continued to live my own life.