Thanks for sharing the sentimental stories and good luck whittling that lot down to just 3!
Not that my opinion matters, but if it were me I would keep the Oyster and your Grandad's two. You have made a pretty bulletproof case for that option. I would then break the rule of 3 and pick one all rounder that I could live with getting scratched, either from the collection or with funds from selling the rest. I would also use some of the money on doing some nice things with the family because at the end of it all, you will cherish the memories more than the watches...
In any case, enjoy the process.