Sounds about right. Trigger pulls for the 24/7 have been reported from 6 pounds to a little over 8 pounds of pull. Individual massed produced guns are going to be different, even if made by the same maker. Kind of a rule of thumb. Doesn't matter who the maker is.
Why not go with a PT1911? SA pistols would help and have the shorter trigger pull as well as being about as light 24/7s SA/DA.
On the arthritis, this is a case by case basis, as some can use the 24/7's trigger and other with worse cases may not.
One other thing. Are you folks able to rack the slide ,or is going to a 9mm. with it's lighter recoil spring, or even a lesser caliber a good idea? I would think that if pulling a long trigger stroke is going to cause problems, then racking a slide with a powerful.45ACP recoil spring would cause agony.
There are lighter springs, but these can cause fit and function problems from the get go.
If the lighter springs do work well. Softball ammo would be all that one might be able to shoot.
Certain forms of arthritis are dengenrative and move quickly. Others are not. Know of a gent who is down to shooting a Ruger MKIII or a Hammerli Trailside in .22lrf because the degeneration advanced fast enough to keep him from being able to shoot centerifres.
This stuff hits at any age and can debilitate people fast,at a slow rate, or not at all.
The trigger pull on my PT111 in 9mm. is much shorter than it is on the Ruger P97. At least in DA mode.
So a 24/7 in 9mm.,whether in full size could very well be the answer.