Communion/Sabbath Works as such.

Communion Master's are boosted in ALL magical paths (including Holy/Unholy) based on the number of Communion Slave's are on the battlefield.

The Modifier for this is:
2 Slaves = +1 Path
4 Slaves = +2 Path
8 Slaves = +3 Path
16 Slaves = +4 Path
etc.

Also, all spells cast by the Master have their fatigue attributed evenly among the slaves. So a Master casts a 100 Fatigue Spell, and they have 4 Slaves. The Slaves each get 25 Fatigue and the Master does not gain any.

Any single Buff type spells cast by a Master affect current Slaves. So if you cast Quickness as a Communion Master, the Master + all Communion Slaves would be buffed with Quickness, even though it is a single self-target buff.