I have a spreadsheet that has everything... when I purchased a given poster, from whom, how much I paid for it, where it is physically located, for each of my 13,000+ posters. I have an addendum to my Eatbrie.com website (not listed because it would be obnoxious) that lists every poster worth more than $500 (the lowest price worth insuring). It has the price I paid and the price it recently sold for. This is all my heirs will need to know to not get robbed.
This being said, I strongly believe that collecting posters is a hobby and I would hope collectors don't put all their eggs in the same basket, because their heirs might be slightly disappointed. There are zillion better ways to park your money and make it grow. If movie posters are your kids future, good luck to you and them.
T