If you want to house parrotlets together, no matter the sex you need an extremely large cage. They house better in an aviary setting. These are very reactive and emotional birds. When they have an outburst is can escalate to very serious fights. The cage territory becomes very precious to them.
I have two boys, they are housed in their own cage. Each birds has his own flight cage. Sometimes they can play in the common area nicely. I have noticed it depends on the time of day. Midday is a very emotional time for my parrotlets, they do better out together in the evening. Though more often than not they fight. The problem with parrotlet fights is that neither boy wants to back down. They just continually react to the other and it intensifies. Males have killed their female mates before when housed in close quarters. So please keep it in mind. This species is not monogamous through life, they change mates. So sometimes they disagree with the human's selection and they want a divorce after a few seasons.
My parrotlet Neptune is very loving to other birds compared to my partner's parrotlet Picard. One day Neptune flew onto Picard's cage, trying to feed him. Picard bit Neptune's toe and wouldn't let go. Neptune was in a mad panic and before I could get to the cage to separate the fight. Picard had dislocated Neptune's toe and there was a pretty gnarly cut on the poor toe. Thankfully it wasn't broken. So the toe was realigned, the inflammation went down, and Neptune made a full recovery.
Did Neptune learn not to feed Picard? Nope.. he still thinks Picard requires some good home cooking. However Neptune is a little fearful of Picard.
I will say I think it is still better to have a few birds. Even though they aren't the best-est friends of all time..they still are flock mates, and chat to each other all day.