My mother owns a mobile home on her property. She started many years ago allowing a family to live there for $100/month to help them out for a short period. Now it has been ten years and she wants them to move, but they say they do not have any other place to live. For the last year they have not paid any rent.

How can she evict them in the state of Alabama? They have now changed their mailing address (gotten a P.O. Box she supposes).

Yes, she gives them a 30 day notice to move.

If they don't, she files for a eviction in the court. You go to a hearing, say they are behind on their rent, if they don't move out, the sheriff comes out and thows all of their belongings to the curb.

This article:
http://www.msplaw.com/pdf/newsletter_vol2_iss1.pdf
May be helpful with the specifics. If they are not getting mail at the property, have someone go with your mom and witness her delivery of the letter. Take a picture if necessary.

If they don't move and she has to evict, then the sheriff's office will serve those papers, though there will be a fee.