With my experience with water dragons, they are little monsters, especially with food and I'm not sure 3ft would be enough space for four lizards. I have no experience with Frilly's though so I'm not sure about that...
And they're two species from different sort of environments, I don't think they could all be happy for a long period of time. Like I said though, I'm not sure with the Frilly's so hopefully someone here can give you more direction
Why do nearly all your threads consist of you wanting to stuff as many animals as you can into 1 enclosure? How many times do you have to be told certain animals shouldn't be housed together, let alone in the enclosures you want to? Do you really not get the hint.. If you cannot house the animals properly then stop dreaming and don't bother with them.
Don't sweat it Magruber, but have a think. Water Dragons require a humid environment whereas Frilled necks not as much, a hotter slightly more desert terrain is what they would be suited to. Good luck with it all!