If your husband enjoys a good book and now has difficulty holding one, try audio books he can listen.
There are also book stands or tabletops to fit over chairs. He may be able to read from a book placed on a table top, desk. Enquire at a mobility shop.
You say strong tremor in hand and legs. Has he a arm hand not effected by tremor ? I have a tremor on my right side, I have learnt to use my left hand to type on the computer takes practice.
Walking is great not only exercise but gets you out in the fresh air, meet people , visit places.
Not being able to walk skips the exercise but with a scooter wheelchair you are able to get out and about.
Chair based exercise too.
Yes, some things have to go on the back burner but ADAPT is the key, chat to your doctor get referals to professionals who can help and support you and your husband.
Try not to give up, there are ways to help you, take a deep breath and see what is out there, when I feel down the best advice I receive is 'think about what you can do rather than what you cannot do’
Its tough and you need support, best wishes. X