I think the main problem is the holes are to deep. You just need the
holes deep enough to get below the frost line. If I were you I would
find out what is recommended in your area and refill and pack the holes
to that depth.

If 5' is recommended then just go ahead and do like the other poster
said, drop your sonotubes in trash bags into the hole, fill with
concrete, and put the post anchors on top of the pillars while the
concrete is still wet. I wouldn't sink the posts in the ground in the
concrete as you have a lot of moisture in your area.