"never be sold" and "grandfather" are the keys for me.
Can only say what I would do.
Check the internals and fix faults.
First go for fine wire wool with oil and lots of elbow grease on externals and see how the result suits.
Re finish is the last option 'cos it's not really reversible.
Bring grandad back into it by thinking what he would have done.
I would be delighted to think my grandchildren would like to work on any of mine.
Whatever they decided would be fine with me.
Here's one they may well have to finish for me!
A couple given the full works which may help a decision
Keep us informed please. Pictures! We luv pictures!