People do this all the time. You should be fine. I'd rather do this than have some yard haul my boat. I hate the feeling of seeing my boat suspended by old straps with a 19y/o kid driving the travel lift.
All that water in your tanks is to the good. If you find you need to "move" some weight around just turn on the tap and empty a tank or two.
Faster, the idea of tying 2 boats together to careen is novel. Scary, but ballzy.... Not sure I'd try it either. I have visions of them slipping apart and tangling their masts together.