I've done it with my 4! I'll admit yours are a bit younger than mine were when I did, and they were very familiar with the parks. But like you, we have traveled without DH since they were infants. Just take a lot of time to prep them about the crowds & rides, plan for bathroom breaks in the family bathrooms, etc. Also, get them each a dog tag with your contact information and teach them how to identify a CM vs a "stranger". Last advice is to get them all matching shirts, even if just plain tees. It really will help you keep track of them, and if you do get separated (always my worst fear), it's easier to say "looks just like this, but bigger/small".
You can do it!