Our trip is early June with my husband, two 10 year old daughters, and me. Our current plan is 3 days at MK, 1 1/2 day at Epcot, 1 day at HS, 1 day at AK, and one resort day (Poly). My husband loved SeaWorld as a kid, so we started talking about Sea World. Would you drop a MK day to go to SeaWorld, drop the resort day for SeaWorld, or neither? Our family is split - two of us want SeaWorld and two of us do not.
I'd keep Disney. Have you been in the summer before? It's hot. Now, we totally didn't find it that unmanageable. But we're used to humidity. My BIL and his family went to SW in the end of May, and honestly, couldn't handle it. They left. It was too hot - there's just not as many places to get out of the shade or into A/C as there is in Disney. So that's their story - spent almost $500 for 3 or 4 hours.
For us, we originally planned on doing SW, because DH and his mom really wanted to go. Yeah, the kids would have enjoyed it, they would. But... I'm not a big fan of SW due to the orca captivity, and how damaging it is to them. Yeah, Disney has animals in captivity, too, but you can't begin to compare AK to SW. It's not even remotely the same concept. They're also struggling big time, admissions were down 12% last year, and San Diego SW is actually closing it's orca show next year. Orlando is supposed to be creating larger tanks for them, because they've finally acknowledged (via pressure) that their housing facilities are inadequate. So, there was that.
But really, even aside from that... once we got to Disney, we had no desire to be elsewhere! We spent 3 days at MK, 2 days at AK, 1 day at EP and 1 day at HS - and didn't even come close to see everything, even just the things we wanted to! So, I definitely would NOT drop a Disney day! But, if your DH really wants to go, then maybe he can go with the child that wants to on resort day, and you can stay at the resort? For the record, I would also not drop the resort day. Disney in summer heat is exhausting. You'll need the rest. Otherwise, you'll get burned out.