Do the robots have to be fully rested so for the middle platform can it be hanging off.
No, I don’t think so
So they can’t hang or they don’t have to be fully rested
No need to be fully rested on the Center Platform as long as they’re touching the Center Platform and not either Alliance Platform or any field tiles or white tape.
I don’t think it can hang off, as that would require attaching
Please don’t claim physics says that.
who said you have to make the robot the max size allowed by the rules 
Who says your team mate cant lift you and then park up there while holding you???
edit:
maybe there is an expansion rule against it but long as you keep your height under 18 in I think you are fine.
Just make sure when they lift you that you have some part that you can maneuver to touch the Center Platform.
Interestingly, the VRC Hub app allows for 2 robots from one alliance to score on the upper platform. More interestingly, perhaps is that it allows 4 bots to score on the top platform.
https://lh3.googleusercontent.com/arGkfHmrUGB7-Nk6DBafNg_OjofWUtHCuAQaSCXxWrtc_0jxO-crs-zV44YkNwhAMQXjgCflT5pIqbZs2g-s238Wj-f1rXhvUplIUBvCa9y1ZjuxQHp4Z_LzkuJ2aw5GgESXkYLtcKZE4MVCPljWb3lKuGtzvgTVhYQfEqzB-HLN9hSLYmBjr78C-4JT1h02La2k99T-HI_vSpZUugUszjEuyYep0QAi4BrkQ7BWun0J21fOQZYp4OxR01AFfi5Ce1AM8G_zRWswVCNBB1kqBIBuwnhMctl0yawNoaAdu9svLTc70QoJjJ4xeVfOdn0xyLMwDB3itPkH5oyQ_qnYnFI1Dj86NzkBT4A4-m9LQR26QumBt3vQ1GjHZwwn7avoJ1vQOLRiwFU2YoYvHN6pxKjBUN1UyEVw3Iw8YB2VCvp25I8b9qsMrra3A3tsi0RcVzyYMZbd5Y_Q-p9gqBg1HomXSjwzj33PLIDKo2pFUdxczkWcL4vMzY8mDRrF8ldh5eDSShqJg3svf0QlLE2d8wO2wRDpINtwS-8wmz_LlwwtQCJmOCjKf66Gt7Wkk5UKqxODMjb364AFI6c5hx65zFvnS2yGbJKLIhyCbCBr-PBuLAosBdjZd7Li1dyDdSzz5DgCCSr9MvtVy1ZdybVCi_lEhAZ_qHEZ=w358-h635-no
Have a dangling string that just drags around. When lifted, it just falls and touches the platform. Problem solved 
Oh, sure. I’d thought of the same. You just have to do it, and you have to make sure that the robot isn’t too tall when it’s picked up and the string dangles.
If it fits, it scores. – no?
Wait. So you actually can have your whole alliance on the platform and get 12 points?
I find that hard to believe.
Why? I don’t think there is a rule that says you can’t. It’s not easy for two average 18" square chassis robots though.
Just make a large wedgebot… Have the alliance climb you…
You and your alliance have to be touching the platform
I never said the robot has to be * completely* on the alliance robot. You can still have the back wheels of the robot touch the platform. ¯_(ツ)_/¯
Tru
Oooor, you could stack the robots on top of each other on the platform