Three ways.

Option 1. Do them solo, "the hard way". Drop group, get companion. Drive The Struggle Bus.
Option 2. Level with 3-1 or 2-2 group make up. I.e. (1) toon isnt the same class. (The drawback here is that you have two storylines to do now.)
Option 3. Level two groups / teams at about the same pace, and interject to help one another. (the drawback here is obvious)