Mithran, Heirmund goes before Lehko (in fact, he goes first out of everyone). So, you have a choice with the colour spray: either angle it so it does not catch Lehko in the AoE, and only reach 2 goblins, or risk including Lehko in the cone and get all 4. The way you've worded it, unless you say otherwise by the time I post in about...seven-eight hours, I'm going to assume you're risking Lehko.
And note it's the 5' step back that causes this issue. If you could stay beside Lehko, he'd be fine. --Of course, then you'd catch Terrek and Jair in the cone...: )