I’m not sure what it’s called, buy I love the trope of where a large party gets split off into two smaller parties who eventually reunite. This split could be forced through physical events or it could just be a relationship split between friends.

Lord the Rings is a great example of what I mean. Frodo is forced to leave after seeing what the Ring does and Sam goes with him, while Mary and Pippin get kidnapped and have their own adventure, and finally Aragorn and his merry trio go help the war effort in Rohan. They all end up reunited in the end though.