Thank you for all the responses.
I am 57 and DH is 64, DS is an only.
All the people I would automatically ask are in Ireland and we are in the UK, I was going to ask my cousin who lives in Middlesex if his eldest daughter would be up for it, then I asked him how old his executors were by age I reckon one of them, by his answer was his really sensible daughter. So I don't think she will want that job twice.
Off to have a think.