User blog comment:BlueBarracudaMary/Protagonist, Deuteragonist, Tritagonist, Tetartagonist, Pentagonist, What Comes Next?/@comment-34345389-20180225033636/@comment-961279-20200131161752

That's not going to work, either. Given your previous definition that deuteragonists are "two equally-important main characters", tritagonists then means "three equally-important main characters". There are 11 other members of the Loud family, not counting the pets, so eleven people can't be in a classification of three equally-important main characters.

You'd have to change your definitions to the other meaning so you could say Lincoln is the most-important character, Clyde is the second-most important character, and all of the other Loud family members are third-most important.

This is another example of how trying to line up characters side by side and putting a label on them to show their rigidly-defined level of importance is counter-productive and useless.

Keep it simple. Main character(s), secondary character(s) and minor character(s). Then you don't have to waffle back and forth between two different definitions in order to make them fit classifications that no one can agree upon anyway.