Hmm, I'd DEFINITLY get another bird, if you get a bigger cage. It doesn't have to be huge, since their cage door is open all day long.
I actually would recomend the cage that BetsyDaisy has. It's 18x18x30, which is only recomended for 2 keets, but your guys get to be out all day long.
The cage is also wider than it is tall, which is good for keets considering that they fly horizantaly, bot verticaly.
The cage you have now, really isn't good at all...no matter how much time they get out of the cage.
Circualr cages are also not recomended because they make keets feel unsafe.
I would get another cgae, and then another budgie, because as MTLJ said, 2 females and 1 male is a huge no-no. DEFINITLY get another keet. It is alos good to have keets in even numbers so that everyone has a preening/feeding partner.