Need help finding a children's/young adult's book series

A long time ago, when I was in fifth grade, our teacher read us a series of novels set in the 19th century about siblings who were given up for adoption by their mother because she could no longer take care of them. The first novel deals with the eldest sibling while another deals with one who ended up fighting for the Union army in the Civil War. There's at least one other book where one of the male siblings gets adopted by an abusive dad with a spoiled brat for a son.

Does anyone have the slightest clue as to what I'm talking about? If you could point me in the right direction I would be eternally grateful.