I would be hesitant to mount 2-RTT's atop a trailer even if you could. You'll be adding ~300lbs...to the highest point.
I don't know how old/big your kids are but you might consider the Kamparoo that is for sale if you need to buy something soon...Queen size bed could be used for Mom & Dad and a small child and then put 2 or possibly 3-small kids on the enclosed floor. Or if you are camping in one spot for more than a night you could zip on the extra room enclosure for more space.
Or wait until AT gets their hybrid/clamshell/Ateroo done .
1999 Toyota 100-Series Land Cruiser...not nearly stock
2009 Kimberly Sports RV 'King of the Offroad' trailer: Sadly gone but it sponsored some of the best memories of anything I've ever owned!