Objectively, Relkhiras should also perform well in a group; he has AoE attacks.
I just don't know if he'll go on a quest without his friends, and taking all three Heroes might be a bit risky (the weak point is Kataviana).
Subjectively, I want him, but I can't be sure if he's the ideal option for us.
Added 2 minutes ago
Regarding Hekkelia, I think one of them will definitely win the conflict without us, so theoretically, the main thing is to GUESS. Then there shouldn't be any complications, unless they send the squad straight into the thick of it without support.