Are you "into" trains and understand the value (or not) of your Father-in-law' s collection? The reason I am asking, if you do not have an interest or do not know any perceived value, you are going to be heading down a dark path for sure to try to liquidate on your own.
My opinion...if you have no interest yourself, contact one of the auction houses and let them sell everything for you. Some will even just give you a check and take everything. Be prepared for "reverse sticker shock" when you see just how little the older trains are worth unless they are rare, mint and in pristine shape.
As soon as you publish a list, any of the "good stuff" will be gone, cherry picked over, and you will be left with a lot of boat anchors. However, a list is a good thing if selling everything at once.
Donald