Both are amazing choices, congrats! My son was talking with both schools earlier on in his recruiting and visited both, but neither ended up recruiting his position this year (he’s likely committing to a different NESCAC). As far as Brunswick versus Amherst, I don’t think you can go wrong either way. The college town of Amherst is right there and it’s right next door to UMass. However, Brunswick looked like it would be fun too (in a different way). Plus Portland (really cute city on the water with amazing food) is only 45 minutes away and you could also take Amtrak to Boston and be there in 2 hours.
Something to consider is getting to and from both schools from Hawaii. My home airport is Hartford (aka Bradley) and it does not have any direct flights to the west coast (except Vegas), much less Hawaii. Most people here who are flying to Hawaii from here typically fly out of NYC or Boston because there are better options. I know Brunswick, ME has a coach bus that goes directly to Logan airport in Boston, not sure if Amherst has any buses that go to the airports in NYC or Boston (they do have one to Hartford though). Just something to think about. Good luck!