Hello spades928, welcome!

Sounds like you have a bit of history there and stamp colelctors usually like stuff with history.
Start a topic on the main forum where lots of people can see your stuff and scans or photos will help immensely in determining what you have is so-so or really nice.
Condition is all important (usually) in stamps and covers (envelopes).
As for selling, the more you know about the stuff you want to sell the better off you will be in knowing how to sell it and what to say to attract the people who would be interested in it.
It may be specialized and not seen very often on
ebay or Delcampe or elsewhere or it may be somewhat common and you just didn't know what to search for or know how it was usually sold.
Lots of variables.