Look at saddle tilt, should be between flat and 3 degrees tilted down. Although each saddle varies.

Try a different saddle, no saddle is perfect for everyone. I think many people adapt to their saddle, but if he is starting to have problems, a change might be worth a try. I like a firm saddle with a cut-out.

Good shorts, or even better bibs. I wear Assos, worth every penny. Nice chamios, stays in place, excellent quality.

Ride harder. Pedaling harder will transfer more weight on the legs and off the butt.

Good luck, hopefully he will find a set-up that works.