I could write a book on what you are about to learn. Your first knowledge will come when DH is fitted with his prosthetic leg. Will he take to it and find his balance? Time and therapy will tell.
I didn't find my balance. I tried. So I walk with a walker for short distances, at home I use my wheelchair because the walker bangs into everything and you can't use it and carry anything at the same time. Outside the house I have a
scooter in the back of my mini-van with a scooter lift. My mini-van has power doors which helps me. I paid for my scooter and scooter lift myself. At least with a left leg amputation, DH should have no problems driving as usual. Make sure to get a handicap tag.
If DH goes on SS Disability, then in 24 months he must go on Medicare. Medicare will not pay for a scooter for DH if his ailment primarily is about his leg amputation. You have to have upper body weakness (like stroke or MS, for example) for them to help with electric mobility devices. All they will do is furnish a wheelchair. Those TV ads are extremely misleading, and don't ever, ever, call the companies with TV ads. They use high-pressure sales tactics and overprice their products immensely. Do your shopping through local medical equipment stores. Compare their products to buying them online and saving more money. I use Spinlife.com. !00% reliable, and best prices.
Getting to your question. If your DH finds his balance and walks somewhat normally, maybe moving ramps won't be difficult. But only a few months since getting his first prosthetic, his stump could be sore, and he may be given only a beginner's prosthetic, which is not a great help to proper walking. I say this because the prosthetist can't predict DH's success/failure with the new device and may alter it continually, searching for what works for your DH. Also, DH may gain weight with his amputated limb, and need a new prosthetic in just a year.
I am going to bet that your DH will not do well on a moving ramp. Peter Pan will be out of the question. You need to be ambulatory to ride. Same with the Wedway People Mover. Both rides, they will not stop the moving platform. For Haunted Mansion, go to the Handicap entry (which is the exit). They can stop the moving platform if you say your DH can't handle it. They will also stop it for you to exit. POTC is not bad. BTMRR is not bad. Spash Mountain is a little difficult but doable (and worth it). Space Mountain -- forget it altogether. See my thread a few days ago about my disastrous ride. I would say Swiss Family Robinson is out. Jungle Cruise is doable. The speedway cars, I don't know, I would say forget about them.
At Epcot, Test Track was tricky to get out of. I have kind-of retired from that ride. The Maelstrom I didn't bother with. At DHS Rock N Roller Coaster they have handicap cars that differ in that they have doors that open. This really makes all the difference in getting in and out of this ride with an amputated leg. It is still a bit of a head scratcher, though. You'll find out what I mean. I'm trying to say that beginner prosthetic knees are either locked straight up and down, or unlocked and can't hold weight. So some rides you have to think of what to do with that half-useless leg and where to put it so you don't collapse it. AK is OK, can't think of anything offhand.
As far as what you can do to assist, you have to follow along with what DH says. Everyone is different. And he will be learning, and maybe changing his mind from day to day and hour to hour. I have encountered plenty of people who held out their arms to help me but truly, I look for a railing or the side of the ride because I have been known to bring people's arms and them flat to the ground by leaning my weight on them. Railings, not so much. Best advice: keep a smile plastered on your face (takes practice) and be ready to laugh instead of cry.
