ML, you're still at a stage we've managed to overcome with difficult child 3, at least in part.
Manster does need to get out more and socialise, especially doing things he likes or is good at. But I can also understand the need sometimes to back off.
First and most important, never turn it into a confrontation. Always involve Manster in the choices. But if you don't ever say, "You MUST do this," then letting him back off isn't letting him win. ONce the thinking gets to the winning/losing stage, the war is over and you have all lost.
difficult child 3 just came in and added his comment. "Yes, it's easy to get into habits and always do the same thing in the same place at the same time. But sometimes even I do want to be among other people and if I make the effort I do enjoy it."
I've mentioned before, the 'trick' that SIL1 introduced while we were on holiday together in New Zealand. We were in foreign territory, with different foods to try; but difficult child 3 didn't like change too well, he wanted the same food he got at home. There we were on holiday and difficult child 3 wanted me to cook a large batch of his favourite bolognese sauce that he would LIVE on given the choice. Eating out (which you do on holidays) was a nightmare - difficult child 3 was ravenous, but his menu options were very limited.
SIL1 introduced a game (I guess you could call it) where difficult child 3 had something available that he liked to eat (chicken nuggets for example) but we asked him to have a taste of the new food (kumara fries for example). The rule is - have a taste. Yes, you can have a glass of drink available to take the taste out of your mouth if you don't like it. No, you don't have to have the new food for your meal if you don't like it. But think of this, difficult child 3 - what if you had never tasted chocolate, or strawberry? What if you were too afraid to try it? How many years would pass, before you learned how yummy something could be?
The next thing difficult child 3 has to do is tell us, after he's tasted it, what he thinks. Of course the initial reaction always is, "Yuk!" But you don't stop there. Its OK for him to say, "I don't like it." But he must say WHY he doesn't like it. What is it about that food that you don't like? Is it the texture? If it's the taste, what factor of the taste don't you like? Is it too salty? Too sweet? Too bitter? Too spicy? Often as he tries to describe what it is he doesn't like, difficult child 3 analyses it and realises that his instinctive reaction is talking, and not truth.
We were in New Zealand for a month. By halfway through the trip, difficult child 3 was trying a new food at every meal. About half the time, he liked it a lot. By the end of the trip difficult child 3 was ordering a meal in a restaurant and calmly explaining to the waiter to please not give him gravy or sour cream or onions, but otherwise bring him the chosen meal unchanged. It was a huge breakthrough for us.
Another thing you can use, a technique difficult child 3's therapist is using on him right now - the new experiences spreadsheet.
difficult child 3 is a computer nerd, and will happily organise spreadsheets for this or that. Every year for Christmas or birthdays difficult child 3 will set up a spreadsheet of what he wants, how much it costs and where it can be found. He sets up another (password-protected!) which lists what he bought for each person and how much it cost.
So we got him to set up a new spreadsheet for experiences. The rule from the therapist is - you must have two new entries between appointments (that's one entry per week on average). Each entry is a new experience.
The headings are - the experience itself. difficult child 3's belief/concern about the experience ("I will be laughed at. I will be afraid. I will be sick."). Then the experience itself, now he felt at the time. Then how he felt after it was all over, and whether his expectations were real or not. You could also include a column for what he liked about the experience and what he didn't like about the experience.
For example, we had tickets to go see "Mama Mia" on stage. difficult child 3 was NOT wanting to go, he really fought hard. But we weren't going to waste the money. However, we were also concerned that one of us would have to take him out of the theatre, which would affect our enjoyment. difficult child 3 talked it through with the therapist and explained his fears that he would be afraid, or he would be bored. We discussed what he could do in each case. We discussed what he would be afraid of and how he could handle his fear - how real would the fear be? We also noted that difficult child 3's DS helped him cope, so we let him bring it with him. We let him play it at the restaurant table (the restaurant was noisy and crowded, the DS helped difficult child 3 feel grounded and calmer). We let him play the DS before the lights went down in the theatre.
Outcome - difficult child 3 was calmer to begin with, because he knew that if he got scared he could close his eyes and block his ears. He also knew that nothing would really hurt him. We also pre-familiarised him to the music and the story line, so he had some idea of what to expect. Because difficult child 3 was calmer, he had more chance of staying the course. As he did - the music hooked him in, it is such an exhilarating show. So when he wrote up his spreadsheet, he was able to say, "No-one of my fears were true. I loved it, I've now seen a live stage show."
We have talked tis through with difficult child 3 and he knows he needs to have one new experience every week. He knows he must take one risk every week, a risk he has discussed with us and that we approve him taking.
For Manster, going to tennis is one such risk. Get him to write down a list of new things to do and what his concern is (if any) about each one. You can modify this method to suit, perhaps include a category of reasons why it would be good to do whatever it is ("If I go to tennis, it means Mom & Dad get to spend time with their friends, with me too as one big family. It is good to do things as a family.")
Also build in an escape option - if it gets too difficult for Manster, can he go sit in the car for a while? Or can he be the one to go fetch out of bound balls? Give him a job to do, or discuss with him ahead of time what his fears are and how to minimise them.
Don't be tempted to use tis method in a less formal way - from what you describe, the situation with you, husband & Manster needs something formal like the spreadsheet. It needs to be in writing and you need to follow through. Doing it in your head will be far less satisfactory and far less effective as a result.
What is needed, is success. The best way to have success is to set him up for success by building in escape hatches in case they're needed and pull the plug BEFORE there is a problem. Then you can look back on the afternoon at tennis and say, "We had fun for a few hours, you played two games and scored well. We left before we got too tired and we left still wanting more, so we'll organise to do this next weekend too."
Also as difficult child 3 looks back over his spreadsheet, he can now see a large number of experiences he's got under his belt. HE can see the evidence of how scared he was (he can scarcely believe he felt that way before) and can remember how much he enjoyed the vast bulk of it. For the experiences he did not enjoy, they are now outnumbered by the good ones. And none of his worst fears ever came true. Having it in writing makes sure it always stays in perspective.
Make putting it in writing, a condition of getting out of the activity he doesn't want to do. This time. But he has to take up the challenge. He can control the list of new activities, he can choose activities to do. For difficult child 3, watching a movie he has not seen before, is a big risk for him. it gets listed. Or reading a book he's not read before. Or writing an essay, or poem. But each time he accomplishes it then looks back at what he wrote about his fears "I can't do it, I will make it look stupid" and then sees that he succeeded and it was easier than he thought- success breeds more success and optimism.
If tis isn't clear, let me know. We've come a long way thanks to difficult child 3's therapist and I'm happy to share as much info as you need.
Marg