Is it better to stay in Sorrento or town
Of Amalfi if husband has mobility issues?
It really depends: what day trips do you want to take?
Plan on staying local around hotel 2 days & hiring a private driver for 1 day to see as much of coast as feasible.
Sorrento is basically flat in the center
Amalfi is not
Another option is Salerno which is mostly flat
If you're only visiting the Amalfi Coast then stay in Amalfi, Sorrento is not on the Amalfi Coast. Amalfi Town is reasonably flat.