You might also check how the door was planed (sanded down to be level with the frame and floor). If that is off..the door won't open either. Then of course..the paint! We had one painter who painted the wooden windows in an older home shut! They stuck too!
Best of Luck to you.
Gail Mercedes Cole
I would get a foundation ispection. The company I use is The Foundation Works. They can determine if that's the problem. There are a lot of other reasons why the doors would stick. Old doors can stick when they have too many coats of paint for example. Before you invest in a foundation inspection you might want to get a general inspection.
The Carrabba Group
Keller Williams Wilshire
OR could be nothing doors could have been freshly painted, YOU CAN INSPECT / search for cracks above doorways, windows, check brick on exterior of home determine if any cracks repairs.