Hey olafinski,
My husband's oldest also struggles to just "jump in" with new kids at events and have fun/relax, though her younger sister does fine with making new friends. That can be painful when you'd like your child to have a great time with peers, yet you see them struggle to connect, or to get involved with groups where they could have better chances of making friends.
OK, so, we can work with that. Sounds like "forcing" your kid to join a group won't go well. That's OK, there are other options to get you and the kids away from Mom for a while and build great memories and have positive experiences. (I am rereading your post, you just have your 10 year old son with you, right? No other kids -- at least on this trip?)
I wonder if there are any "day spa" or "wine and painting nails" or "relaxation massage" type places in the area you are staying. Could you treat your wife to a day out at the spa to relax, while you take S10 and do some outdoor activities?
We took DH's 2 kids on a tropical vacation a few months ago. My older stepdaughter (age 15), SD15, was pretty emotionally up and down the first few days, and had a kind of nasty and ungrateful attitude. She toned it down by the end. SD13 was able to jump in and enjoy herself right away -- swimming pool, beach, hanging out with family, etc.
It was tricky that they had no friends or cousins or anyone their age there. But they did have each other, and we made sure to pick special activities on a couple of days that each of them would enjoy, even if it was only with us adults
That being said, maybe there are other parent/child duos in your area in the same situation, looking to get out together and do something fun. Consider checking out activities like whale watching, horseback riding, nature hikes, zip line, aquarium, children museums, etc, where maybe another parent and child are in the same small group. Double bonus: one, you and S10 get out of the house and have positive time together without toxic attitudes, and two, maybe you'll run into some new people, including kids his age, to chat with for a few hours while doing something enjoyable.
Of course, I do know this depends on your transportation situation, and budget. But, it's some ideas to get you started. See if you can get in the mindset of: what can I "gift" to my wife to enjoy, while S10 and I do an activity away from her, in a small group, for a long time. It could be a win-win.
Hope that helps, and hope you get some positive, peaceful moments on your trip;
kells76
