I was attacking my opponent with declined ghouls and he then claims that his surviving troops could redeploy after the ghouls conquest is done, before I start attacking with my active race.
I'd say since it says "redeploy at end of turn" that my active race will also be allowed to attack before he can redeploy. Otherwise those units are defending twice in the same turn, which seems unfair.
Does your opponent have any reason for his claim, other than the fact that it would help him? What I see in the actual rules is the same thing you do.