The Children's Hour

I have a beautiful set of books (volumes 1 through 15 plus an extra book entitled "How to Teach Children Through Song." Published by Houghton Mifflin in 1907. Perfect condition, except for the fact that they are over 100 years old!

This is one example of many very old books in excellent condition that I have inherited from a great aunt, grandparents, etc., and I can't keep them all.

Can anyone help me with some ideas of how to sell some, and how to know if I am getting a fair price?

A couple of other examples:
The Rosary, by Florence Barclay (1911)
And some well-know titles, like David Copperfield (1910

One additional question -- showing how much of a novice I am -- if there is only one copyright date, does that make it a first edition?

Thanks so much!