I've also had a lot of trouble with sit bone pain. Basically, once I had my bike fit, it felt like I was sitting on gravel. I've got the Specialized Jett saddle that came with my bike. I don't have saddle advice, but I can share a couple things that have helped me.

Changing the height & angle of my seat, very slightly, helped quite a bit. Like a couple mms higher. Somehow, this changed the angle of my pelvis just enough so that it felt like sitting on slightly smoother rocks, instead of sharp pointy rocks. Sounds like he's been trying this, already, though.

The other big key was finding the right shorts. I spent a lot of time trying different shorts before I found one that was just right for me. One tip- look for high density chamois, rather than thick or thin. I ended up learning to feel for density first when shopping. Then I'd try on the short, squat & feel my sit bones from underneath the shorts. (Sometimes, the prime part of the chamois wasn't actually under my sit bones.) Then, I'd take them home & sit on my bike with the shorts on. (Undies on, tags in place.) Balancing with one foot on the curb, I would sit with one hand between my seat & the bike seat, and feel how dense the chamois felt directly under my bones. (Do I care what my neighbors think? When pain comes in the door, all pride goes out the window.)

Sounds extreme, but I wound up buying & returning several pair of shorts before I found the Castelli Ypro Donna, which has been the ride-saving short for me. Literally. Expensive, but worth it. They make shorts for men with the Ypro chamois. I got mine half price at backcountry outlet. Sugoi has shorts with dense chamois, but it hit me just behind my bones. Specialized makes some high end shorts that feel like they'd be excellent to me.

Also, trying to get up out of the saddle every 15 minutes or so helps with circulation to the compressed areas. I originally tried to do all seated climbing, because my training plan recommended this. Now, I try to stand for at least a minute or two every minutes. Coming out of intersections, and short inclines are great places for this.

Have you checked for overall bike fit? Is his weight distributed? That helps, too. On rough pavement, I use a slightly higher gear than I normally would & pedal a little harder to put a little more weight on the feet, and a little less on the seat.

Good luck!
Blueskies