As far as I know you can only get Sulani mana by inheritance. I have a sim who is the third generation in receiving this trait. It doesn't seem to change or weaken/strengthen by passing it on. No one knows if an update will ever change the trait. Pack refreshes seem pretty dead at this point so I don't expect it to be updated. The life and death patch did make it more difficult to get the trait by limiting all Sulani elementals to be elders. But that's another story. Once you have received it through inheritance from an elemental you can keep passing it on.
Unfortunately I can't help with the question about the signature drink.
1) Sulani’s status as exclusively inheritable seems deliberate, given its cultural and location-specific nature DDD. However, future updates could expand how it’s obtained, perhaps through gameplay achievements or interactions, reflecting its broader appeal compared to traits tied to supernatural bloodlines.
2) If a Sim claims to have unlocked all recipes, I’d expect they’ve completed every possible task except choosing one of the Signature Drink recipes. Without that final step, it’s a near-complete mission with the last choice pending.
