You may need to install pylons deep into the ground to keep it stable from changing ground positions. There are companies that do this but they are expensive. Good luck!

You can definitely jack up the porch for temporary support, remove the upright posts and pour a concrete footer under each one. In fact, if you don't do this your porch will become unusable and dangerous, if it already isn't.

We had a small deck off our bedroom that was falling on one side be ause of construction like you describe. One post rested on a concrete patio below but the other was in a hole sitting on two bricks! We were stunned to see this when the carpenter got the porch jacked up and that post out. We also had a large screened porch that was supported by three round wooden columns that were failing. The center column was bowed almost two inches, but you could not see this unless you looked back at it from way back in the yard. All the posts and columns were removed, replaced with 4x4 steel columns and then had Azek columns built around the steel. It was. Dreadfully expensive but the house is now FIXED.

Thanks to all for the advice.
-J