Hi Paula! Welcome to planDisney.
As someone who has traveled to Walt Disney World and Disneyland at varying sizes ranging from a 10 to a 28, I have found that Disney theme parks are very size inclusive.
Because Disneyland is an older theme park, some of the “original” rides might be a bit on the tighter side for your son-in-law. It’s so hard to give advice, because everyone wears their weight differently. So, I will give you what I think could potentially cause him some difficulty.
Boat rides like Pirates of the Caribbean,
Jungle Cruise, and “it’s a small world” have a bench seat where I’m sure he will be comfortable. Buzz Lightyear Astro Blaster and Haunted Mansion have ride vehicles that close but allow for plenty of room. Sometimes, I tell the cast member that I’m alone if I want to ride in a seat by myself to ensure that it won’t be too tight.
One attraction where I feel he might have some trouble would be the
Matterhorn Bobsleds. This opened in 1959 and feels like it has been largely unchanged. I find that even at my smallest, I struggled getting in and out of the ride vehicles. Another tight fit could occur on the
Mad Tea Party. Since the wheel to turn the vehicle takes up so much of the middle and the seats don’t move, I find that I feel a little squished in the tea cups, too. I also don't feel so well after all the spinning, so I largely avoid this attraction.
Like I said before, Disneyland is very size friendly. I expect you will all have a fantastic day, being able to ride most attractions with no issues. I have also found that cast members are very nice and discreet should a guest be unable to ride an attraction. Should your son-in-law be concerned, he can always ask the cast members at the beginning of a queue line what the seats and restraints are.
I hope this helps with planning your visit to The Happiest Place on Earth.
Happy Riding,
Tracy