Get a slide scanner and scan the ones you cherish the most. Even at a really high resolution you could probably save about 50 photos onto a DVD burned from your computer. Put the DVD's into a fire safe or safety deposit box with a note about what to do after you're gone. Or perhaps you could donate them to whichever railway historical society you wish.

I hate to say this but I would probably trust a railfan I just met more so than my own family. While I love my family and know their intentions would be good, they wouldn't have a clue what's valuable and what isn't. I've seen this happen to other railfans who have died, all of the good stuff was thrown into the trash.

At the very least, write out what your wishes are and make your family aware of them.