My dear wife and I like the idea of "giving with the living hand", and the second-to-die dying broke. Single Premium Immediate Annuities will be useful in arranging to die broke.
Treating offspring alike in wills is simple, and I think equal treatment is less likely to cause resentment. Still and all, some people have an infinite capacity to find an infinite number of things to resent. We are up-front with our adult children about the living hand and dying broke. I would be very surprised if any of the kids looked upon Mummy and Daddy as their "retirement plan unaware". We keep them advised of the contributions were are making each year to their children's "529 College Savings Plans".