See, I just tried the grappling hook method and the other one just ran up to heal him.
Send your companion to agro one of them first. After he agros, pull the other to you and work him down. That maybe the solution to it.
If I am thinking of the correct mission, is this the one aboard the imperial ship? If so, I did this as a healing merc while using Torian (sp?) and focused down one. Died, then came back and worked the other. Again, if it is the same fight I am thinking of.