Since Hermetic Sorganak ex Miscellanea come from a tradition where their magic has been adapted to the Order, do they need to buy both Magic Theory and Folk Witch Magic Theory?
Also would they have access to the Sorginak supernatural abilities? (Or would they need to take them as virtues?)
They have this:
Necessary Condition (Potions, Euskara Incantations, and Fetishes)
Do they use the Sorginak/Folk Witch method of brewing potions and creating fetishes?
Do they need a separate fetish for each spell? Or each art?
Hermetic Sorginak are hermetic mages, using hermetic magic.
They need Magic Theory for hermetic magic.
They would have little use for Folk Witch Magic Theory, since they aren't Folk Witches.
They would not have any special access to the Supernatural Abilities of non-hermetic Sorginaks - except for the single one they get as their Ex Misc Major Non-Hermetic virtue.
Exactly how the Necessary Condition is to be interpreted is not clear, so you get to decide how it works in your saga, but they would not need to use more than one of the listed conditions (Potions, Euscara Incantations, Fetish) for a given spell, and they would not have any special ability of brewing potions that other hermetic magi don't have.
Some of Necessary Condition is explained under Exotic Casting (p.98). If we then check Incantations on p.94, we see that they work for nearly everything. So incantations should work for Hermetic spells, too. Necessary Condition invalidates the last half of the last sentence for incantations on p.98, though. Theoretically you might use a fetish instead if you want to cast without the incantations, but as fetishes don't work with everything that's more debatable, and it takes a season to make a fetish.
Folk Witch brewing of potions is a lab activity. Personally, I would use that for things like charged objects and Longevity Rituals.
I think the really tricky part comes down to lesser enchanted items and invested items. Creating a fetish is also a laboratory activity, but it only works with things the folk witch can use. Does that mean they cannot make a normal item that someone else can use? Perhaps.
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Separately, Folk Witch Magic Theory is useful to them. They don't use Magic Theory for their Sorginak Supernatural Abilities, of which they have at least one, possibly more if you spend the Virtues to start with more. For these they use Folk Witch Magic Theory instead.