I think your boys will be more than fine. My son was 14 when we all last went and I allowed him to go off by himself every once and a while. Once I had been at the parks for a few days I realized that once he was a little older and with a friend (next time we go he can do this) I wouldn't have a problem with him going off and doing his thing. I think as long as they realize that they need to meet up with you and have meals together it will work out great, and no it's not hard to meet up once apart, I thought it would be a pain, but it was fine. You might have to call a few times to get them since they might be on a ride or in a place to loud to hear the phone. My son puts his phone on silent/vibrate and some times he has a hard time feeling it in his pocket, so I had to call him a few times to finally catch him or his dad (the boys would go do their thing once and while) to see where they were.
I think it's really key that you don't get to strict about them answering right away, or expecting them to meet you at the drop of a hat since they might have just been in line for a long time or on a ride.
As long as my son would call me back in a reasonable amount of time, tell me what was going on and called if he couldn't get to me in the time we scheduled, I was good.