This is why I write down everything when I’m setting something up that’s new to me. Even if I go off someone else’s tutorial I put it in my own words. That way when I come back to it later I’ll understand it and if I run across someone else that’s trying to do the same thing I have at least one step by step guide to offer them.
I’d kind of see that as a bonus. Some time to bond while on a nice vacation on someone else’s dime would be cool especially if it meant not having to deal with the ex and the new guy as much. Definitely don’t go if you’re not going to be civil with the ex and him though (which would be understandable given the circumstances). Ruining the trip for everyone else won’t gain anything other than possibly resentment from the kid.