Triangle party formation

Hey just need help on how to proceed:

If I have a party of 3 characters with the player controlling 1 character, and the other 2 characters are controlled with the AI pathfinding, how would I go about implementing it this way:

The other 2 characters have to find a separate spot each behind the main character to follow.

Basically like a triangle formation!

How would I go about it, including the possibility that they would not always be on an open field so the formation can be deformed? I read the Get Started doc but I just wanna be pointed in the right direction on how to implement it if anybody had previous experience similar to this.