Great story; if they could not get back to the PWC then you probably did save their lives. In 74 degree water it will take a while but it would happen after about 6 hours. I applaud your mom for spotting them and you for getting them aboard; good job!
We had a MOB situation when I was doing a sailing school course. We were sailing off Santa Cruz; about 1.5 miles offshore and as we sailed downwind I spotted a MOB trying to climb back aboard a Santa Cruz 27. He was trying to crawl up the transom and his girlfriend was trying to pull him up aboard. It was choppy with 4-6' swell in 55 degree water; and he was having trouble. So the instructor had us stand by and wait to see if he could get aboard; and she finally was able to grab his belt on his jeans and help pull him up as he pulled on the pulpit with his hands. That was a scary few minutes; even for us as the stand-by boat.