Let the seats sit out in the sun on a nice warm day, and then sit on them.
You probably used too much glue to hold the fabric to the sew foam. You only need enough glue to hold the fabric to the sew foam long enough to stitch around the perimeter of the parts, the lighter the better. I don't use contact adhesive to glue fabric to sew foam, I use foam to foam glue that I know won't hold when the seats get warm.
Nice looking seats.
No one lives forever, the trick is creating something that will.