I have done it too, not by choice though On a 9 day trip I had to go to Maui for 2 nights and it cut into Kauai & Waikiki by 1 night each, plus I wasted time and money going from HNL to OGG to LIH and back to HNL in those 9 days. Thankfully there are 2 OGG-LIH non-stops a day

We go to Hawaii all the time, so it really wasn't a big deal - we've seen all the sights and just go to hang out and relax. This sounds like it may be a trip that will also include sightseeing and other activities, and if that's the case, 3 islands is too much unless they don't plan on sitting still very much