Is it too early to start thinking about Brave 2?
but nothing’s too early for Pixar!
Anyway, here’s my take on the younger siblings of Young Macintosh, Young MacGuffin and Wee Dingwall (Young’un Macintosh, Young’un MacGuffin, and Wee-er Dingwall). They will form an alliance with the Royal Triplets and have an awesome B-Plot Adventure.
Alternatively, these could just be a younger versions of the three lads, in which case my headcanon is that everyone mistook Young McGuffin for a girl for quite a few years. oops! :)