3 SKs seems fair.
I've played a couple of SK only games at a party. Given SKs don't work together like mafia, sometimes they can kill each other off, so it's always best to have more than 2 SKs. But with 12 people, 3 kills in highly excessive. Therefore we introduced incompetent SKs that sometimes failed to kill their targer because they missed them.
I'm guessing at least one of the SKs is incompetent. This explains Debbie's escape and also balanced the game nicely.
Firstly, the choice of Adder seems odd. I can see why people went for Ovi adn Debs as they were experienced players...but Adder said in the signup thread he was returning to mafia after a long break. Usually it's odd when the scum kill a rusty and inexperienced player first night. Maybe someone just had it out for Adder?
Here's what I think:
3 SKs
1 Doc + 1 Backup Doc
1 Cop + 1 Backup Cop
2 Masons
1 (perhaps 2) Vigilante
Rest townies.
Given one townie is already dead, a random lynch today will mostly certainly kill off an important town role, so I'm going to play this day very cautiously...
3 SKs...one bad lynch and 3 deaths tomorrow...could be curtains by night 3.
(Last word: There's nothing against a SK Cop say, or a SK Mason...perhaps the two masons are both SKs but they don't know that the other one is a SK?)