[derefr]

Presumably, if one person called another a "childish jerk nymph", then you have at least one person to fire (the person resorting to name-calling), if not two (the person maybe deserving the label) or more (the people taking sides rather than trying to dissolve the dispute.)

"Fully-formed adults" are people who I would expect to know how to mediate themselves. If people aren't able to successfully mediate their own disputes, then your failure in hiring came long before your latest addition.

Examples of people likely to be fully-formed adults: a mother with multiple children. A schoolteacher. A military sergeant. A nurse. A bartender. In general, people who have been exposed to enough pointless complaining and dispute that the object-level arguments don't matter to them any more, relative to the issue of figuring out what will allow everyone to continue working together optimally.

Note how most of those jobs are service jobs. People with natural talents rarely have to grow up in this way, and the people with the most natural talent are frequently the least grown-up (rock stars, career academics, startup founders). You only see this "fully-formed adult" trait re-emerge at the highest levels of accomplishment: astronauts are frequently fully-formed adults, for example.