The POR pool is set up well for families. If you can generally control your boys, you shouldn't have any problems. The lifeguards are among the best I've run across as well. (They were doing training sessions when we were there a couple times ago and it was hard work for them.) In addition to their safety expertise, if the pool has lots of kids, they'll engage them in pool games (many of which don't require swimming ability).
There are two areas that are shallower with steps to go in. They do connect to the deeper areas of the pool, but you should be able to say "go no farther than this lifeguard stand" to give your boys a line. They'll have plenty of play room. The part with the slide is in one of those shallow areas, so they should be able to enjoy the slide, too.
There are also quiet pools around POR; we've never used them because my DD loves the slide and the fountains at the big pool.
I have only one child, a girl, and she and I are often pool visiting on our own. It's probably not the same as 3 boys, but . . .
Enjoy yourself!