Sub Rosa #13 is mandatory, though there are also quite useful old threads in here if you google things like "diedne virtues and flaws site:atlas-games.com".
Take this one: [url]https://forum.atlas-games.com/t/the-magic-of-diedne/3128/6] and just with Wanderer's post you can define the mechanics of the whole House.
About sacrifices, finally it depends of the take you take of the House. Sacrifices could range from being the requisite of a virtue to boost spontaneous spell to produce ritual effects (which could mean Diedne still being good guys nobody understood: they just ocasionally killed something to do big stuff), to just being part of Chthonic Magic at work (which could mean just dim pagans or slightly into diabolism)... or being the boosting effects of Goetic Arts (which would mean that Diedne House was actually neck deep into diabolism).
Our saga's take, after long debate with our Diedne hiding into Merinita, is the second one. The guy knows Chthonic Magic and must do pagan chants and invoke old goods to use that, and thouh he works better when his hands are covered in fresh blood (special circunstamces virtue) and looks pretty dim (he have dark fae blood and have the Tainted with Evil flaw as an ordeal), he's not actually a bad guy, nor a diabolist (at least so far. He have some concerns he increases his House Diedne Lore and digs deeper into his heritage).