Sorry to hear about your Dad's condition, MRS. Hope he is comfortable, at least.
For your Mum's car, are you looking at buying new, second hand or leasing? Or any option?
If the gatepost is a consideration, I would perhaps steer clear of leasing.
My Mum and Dad (similar vintage) have had an EV for the last 5 years or so and love it. Latest one is the E-Golf.
For a more traditional solution, we found our Skoda Roomster an extremely flexible, practical and economical car. Might be worth a look? If not, perhaps a Yeti?