I have arthritis too .....and 2 things....
1. using the chemical hand warmers -helps a lot /( put one in each pocket).
2. Shooting gloves are too bulky - especially if they have padding ( bicycle gloves, etc ) ....so instead I use Foot Joy golf rain gloves - they sell them in pairs, velcro closures, high tech fibre....they hold up / and you can still pick up a dime. They will give him a little bit of cushion ...and he can still feel the gun - and the trigger - and be able to reload, etc easily.
Here's one source..../ but all the golf super stores should carry them. Golf Winter gloves are thicker ...and too thick, in my opinion.