As with other Animaniacs characters, the Warner siblings were part of a loosely-defined cast of players and often made appearances in other characters' segments, often as a literal running gag, as well as hosting occasional appearances by other characters in their segments.
They are cartoon characters of an unknown species, although Tom Ruegger classified them as Cartoonus characterus. They all appear in the Animaniacs logo, and the show usually begins and ends with gags performed by them. The trio of red-nosed Warner siblings was considered to be the stars of the ensemble of characters on the show. Yakko, Wakko and Dot are the titular main protagonists of the animated series Animaniacs and the 2020 reboot, and the cameo characters in Freakazoid!. ~ The Warner Siblings during the start of the intro.
So just sit back and relax! You'll laugh till' you collapse!