Similar situation for a family wedding when my mum was that age. We were all staying in a B and B and the landlady kindly agreed that she and dad ( mum frail, dad recovering from an op) could stay there all morning, which is what they wanted. They sat in the garden, read the papers, relaxed. We did various errands and brought us all a sandwich back for lunch, then changed and set off for wedding which was at 2pm.
They were rested and not stressed. Lasted the day well but were ready to call it a day by 9pm. Worked well, but they called the shots, sensibly, knowing their limitations.
Hope it works out for you, OP.
How do you acknowledge Easter.