Re: getting to the table?
A wheel chair might work, although I don't think they necessarily pull up close enough to all tables for comfortable eating.
I confess that we no longer eat together regularly at the dining table. Most meals Coy eats in his chair, with a great pull-up table. Coy often takes extremely long to eat and he is self-conscous about it if he is eating with others. I bring him his food on a tray and I eat and go about my business, checking on him once in a while. We go out to eat once or twice a week, and we enjoy each other's company and the experience, but he really doesn't eat much in that setting. We take most of the meal home and he eats it later, when he can take as much time as he likes.
My mother also eats her meals in her recliner (upright, of course) which is a very comfortable fit for her petite frame and easier on her arthritis. She also has a table that pulls up to the chair. It is much easier for my husband and mother to pull a light table up to their chairs than to pull a dining chair up to the table while they are sitting in it.
I bought a nice one-piece stretchy slip cover for my husband's recliner (and mine too). I brush it off with a whisk broom now and then and wash it as needed. My sisters vacuum my mother's chair regualrly with a hand-held vacuum. Naturally if people with impairments eat in an upholstered chair regularly it is going to need some cleaning attention!
These chair-tables are also great for doing crosswords, spreading out a newspaper, serving snacks -- I don't know what either my husband or mother would do without them!
If your father has a lift chair, there may be an optional table for it.
If your mom wants to continue eating with your father, perhaps she could have a similar table and pull it up next to his at meal time.