Hi, Asadmom! My daughter was diagnosed with severe Crohn's at age 11 and we've gone through a lot the last 6 years. It's so hard when they're young. A few thoughts - your son has to be totally on board if he's going to go on the SCD diet. At age 12, that's somewhat unusual unless he's very mature and motivated. You can work hard providing him the right foods but if he doesn't stick to the diet in school or out of the house, the diet can't work. He has to be ready to do this, and do it right.
I'm no expert on the diet, but I believe it works for some and not others, or not as well as they had hoped. This is not something to try for just short-term, as it can take some people a long time to see any results. You can't expect miracles. If your son is ready to do the diet, I think you should go for it.
In terms of doctors, I'm not in California so I can't help with recommendations, but if you can't find one who advocates the diet, just do it yourself without the doctor. Right now you have to get your son's Crohn's under control so he's going to have to stay on his meds but there's no reason why you can't start the diet at the same time. Why do you have to even tell your doctor? Don't let your doctor get you down about your son eating properly.
Parenthetically, Humira and Remicade can't be for life since they stop working for everyone eventually.
If you read up on the SCD diet, you'll learn that if you want to see results you'll have to do it strictly and completely. But if your son isn't ready for that - and I'd be extremely impressed if he's ready to do the complete diet - maybe you can have him refrain from certain foods and that'll be better than being on a standard Western diet, e.g. no sugar.
It was very hard for my daughter to go on the diet. She started a year ago, at age 16, and at the beginning it was hard not to be able to eat any of the food her school gave out or served, and not to be able to eat like her friends or the rest of my family. My friend's daughter refused to do the SCD diet until she was in her early twenties and felt ready to keep it. So if your son isn't ready to do it, don't feel down.
Good luck with everything! Right now is the hardest time, soon after diagnosis, but things will improve and stabilize, G-d willing.