Spec nading has nothing to do with friendly fire..it means you're in one team, you throw grenade and then you switch to spec/or other team before the nade blows and that will give you kills. So to answer 3rd question, yes. (as far as I know, maybe I'm wrong )
how many the nade hits if whole team would be in spawn and you'd nade them, change teams and nade would hit all of them then you'd kill all. So if you're trying to do this (not on our srv please) you need to be fast so all the nabs don't run away from spawn