So this should be obvious IMHO, but a person I play with is insisting I am playing it wrong, so I thought I'd ask. The rules say under Challenges/Outside Forces:
This says to me that if I charge into a single model unit, like Mephiston, and challenge with my Captain my other Command Squad Marines can also attack him. The reason for that is the "if any". If there are no attacks how can there be wounds?“Whilst the challenge is ongoing, other models locked in the combat can only allocate Wounds to the models involved in the challenge after all other enemy models that are locked in that combat (if any) have been removed as casualties, even if the models fighting in a challenge are the closest models.”
Excerpt From: Workshop, Games. “Warhammer 40,000 (Interactive Edition).” v1.0. Games Workshop, 2014. iBooks. This material may be protected by copyright.