Depending on condition, you might want to have some of the more valuable ones graded. Here is a link with some ideas: Vintage Graded Baseball Cards
These sell individually on Ebay, auction sites, private sales, etc. I have a detector friend that collects them. If you just want to sell them in bulk, let me know and I'll see if my friend is interested.
As far as grading goes I would use Beckett grading services or PSA grading services. These 2 are the most trusted and are the most sought after. Both are very reliable. As far as selling goes , try not to sell to a dealer , the will pay the least because they need to make a profit when they resell it. 1950's cards still have a strong market so be careful if you don't have much knowledge with them. My advice would be , before you sell them , look them up on eBay , click on watch item and see what they sell for. Even if it takes a month , do your research before selling , it can make a big difference ! If you have any questions feel free to ask me. I bought and sold cards for over 35 years but no longer do because the market isn't what it used to be.