When dressing someone the rule always is:
Dressing - bad arm/leg then good arm/leg.
Undressing - good arm/leg then bad arm/leg.
That's really important both to make it easier, but to reduce chances of injury or pain.
When both arms were bad, I had T Shirts or Polo Shirts big enough I could wriggle it up both arms then stretch out and over his head. Then he agreed to move to button up shirts only. I would need him standing and would wriggle it onto both wrists, then wriggle the sleeves up both arms together from behind.