It's not incest but is proper weird.
Surrogacy is not ethical.
Using your dead sons sperms is not ethical
Having a child when you are 68 is not ethical
What on earth is she going to tell the child? Is she going to be mum or grandma?
At least when a man conceives a child at that age the child will have a younger mother. So their father may die but they will have one parent. This child won't have anyone, their parent is already dead before they were even conceived