sixline wrasse
 

Supposing I add them both at the same time would it be possible or even a good idea to keep two six line wrasse's together in a 65 gallon aquarium?

Maybe - they are protogynous hermaphrodites, so one might change to a male and you might get a pair on your hands.

I think one of the breeder's challenges on MOFIB is the sixline. Maybe you can check there on how to pair them.