Do you have hoppers? If so, you can go to another park in the early part of the day, and switch to the EMH park shortly before EMH begins. My experience has been that EMH themselves are great. There may still be plenty of people around in the park, but only guests can get on the rides, and that's great in comparison to the way things are during the day. A lot of families are tired and done by EMH times, so no, it's not like every resort family will be there at all. Plenty will have chosen another park that day, and not have hoppers, as well.
The issue with EMH is not that the hours themselves are too crowded (although for the first portion of evening hours you will have to wait for the lines to die down, as those non-resort guests already in line when EMH started don't get kicked out of line, of course), it's that the non-EMH part of the day is rumored to be more crowded. I haven't gone enough to evaluate if that part is true. But we certainly have enjoyed the hours themselves- much shorter lines. I do recommend it for your 3 teens.