I didn't know you could do 'liberty' with Bengalese. I've only heard of it with Firefinches, Cubans and some softbills like Shama but the latter only when they are breeding in an aviary and therefore 'held' to it. (You can do it with budgerigars too, under the right conditions).
I've heard Cubans are social- but no personal experience.
I've heard Cubans are social- but no personal experience.