I think you will find most hobbyists have an aversion to balloon mollies. They have been bred to have a short bodied deformity and balloon shape, and often have swimming problems and die prematurely.
That being said, mollies have large bio-loads, and are generally considered suitable for 29 gals and up. The ballon mollies do stay smaller, but still would need atleast a 20 gallon. I'm not sure if you mean move the adults or move the babies? Adult mollies definitely could not live in a 6.6 gallon tank..most fish can't for that matter. The only suitable options for a tank of that size are bettas, nano fish such as micro rasbora, african dwarf frogs, shrimp, and snails. Or as a short term solution to grow out fry, it is fine.