I'm sorry to hear about your husband's progression.
I would concentrate (but not exclusively so) on your husband's walking: it's free, has little start-up time, leads on to other things, like chatting to the neighbours.
In Stafford (I think Shrewsbury and Telford branches do something similar) we crown green bowl twice a week and also run a physiotherapy class once a week.
The logistics of swimming are difficult for many PwPs. It just takes too long to get to the pool, to get undressed and then dressed again.