Thanks for sharing your DBF's challenges. My DH has lived with Crohn's over 20 years. He's had two major surgeries for the disease. He's been on Imuran for a few years, and it's helped A LOT. If he starts having liver/kidney problems (he's monitored with frequent blood tests), he'll probably end up trying Remicade. He's known a couple of folks who used that as an absolute last resort before a total colostomy, and it changed their lives completely for the better. It's not for everyone, though.
I second the notion of keeping a food diary. I wish I could remember the name of the book, but there's a book out there about dietary control of Crohn's that helped him. He's learned to avoid difficult-to-digest foods. For him, that means no corn-on-the-cob/cooked corn (cornmeal is fine), no celery (strings), virtually no raw vegetables (only a little lettuce and tomato, really). Everything must be cooked, and even then he skips or limits some things (broccoli, cauliflower, celery, and corn). He avoids all fruits with seeds (strawberries, raspberries, blackberries), and usually won't eat the skin on fruit (except for limited quantities of grapes and peaches). Red meat is also very difficult for him to digest, to where we eat red meat usually no more than once a month. He also has to be careful not to eat too much fried food at a meal as well. Actually, he's learned to be careful about how much he eats at each sitting. He makes sure he never eats past the "just now full" point. (This is why we don't do the dining plan -- too much food at too few intervals.)
I'm sure this sounds horrible, and it's been difficult to figure out how to cook so we could all still eat as a family, but every day DH goes without a flareup shows that it's worth the effort.
You say that your DBF simply won't eat in order to either keep from having a flareup or postponing it. The last time DH got really bad (before Imuran), that's what he would do. Poor guy lost 30 lbs in 2 months, looked AWFUL, and had absolutely no energy. When he started the Imuran, he also got some sessions with a nutritionist. She said he absolutely should NOT stop eating! What he needed to do was go on a liquid (i.e., easy to digest) diet on "bad" days. She recommended Ensure, specifically the vanilla flavor. She said the chocolate was harder to digest than the vanilla. Be careful, too -- there are multiple varieties of Ensure. Some have extra fiber (read: harder to digest). Go for as "liquidy" as you can find and drink as many as you need on those days. Wow, did that change our lives! That simple advice even made living with flareups so much better. Where a flareup used to confine DH to bed for a couple of days at a time (which is bad when you get a couple a week!), he would switch to Ensure when he felt a flareup coming on and it would work itself out in just a few hours. Hallelujah!
A large part of DH's learning to live with this disease was learning to recognize when a flareup was starting so he could do the liquid diet/de-stress/relax regimen to let it pass quickly.
Sorry this ended up being long. I thought about PM'ing you and realized that DH's experiences might help someone else too.
Best of luck to you and your DBF. FWIW, with as many "show rides" as WDW has, and rides that even pregnant women can do, and all the shows -- I'd still try to talk him into doing Disney.

Rent an
ECV if all the walking starts to cause a flareup. Pack Ensure in a pack to leave in a locker (you can get cups of ice for free). Plan for afternoon rest breaks to have built-in rest time. There's no place like Disney for making you forget the stress of your everyday life!