Already dead vampires are also unavailable as sires btw.

Yes, it's intended that you can't. If you want to roleplay a Nicktuku, look at Melachoate/Androvikus/Rasalon lineage. They are claiming to be Nicktuku (though a very dubious claim) and are in the mod.

Yeah, I saw them but they aren't the typical Nictuku behaviorwise as in that they aren't inherently evil and want to unify the clan to stand strong against the other clans. So they aren't hunting and killing every Nosferatu they find.

For now I settled with having no Sire which prevents me from profiting from the Nosferatu Legacies but the Nictuku aren't really a part of the clan anyway.

"Typical" Nictuku are the way they are because they are bloodbound to Absimiliard, so they are very specialized tools in his quest, which is not their own. They are extremely anti-social even by vampire standards and generally enjoy very little free will of their own. I'd say in the mod setting their interaction with outside world would be limited to diablerie scheme alone.

That's why they never ment to be playable and only serve as plot devices in canon, along with Antedeluvians and certain other pre-flood vampires. It's not because they are imbalanced in terms of sheer power, although most of them are. It's because they exist and operate in entirely different ways.

Embrace does not make anyone more intellegent. In fact it's traumatizing experience which unlife is full of, so vampires in general are known to be mentally unstable. Just saying, you don't really need to be Nicktiku or claim to be one as an excuse to go full ♥♥♥♥♥♥ about things.

There is a workaround in my experience. Pick a generation 4 vampire as parent, then you get an option to alter your statement to "No, he is my sibling, not my sire." Then you get generation 4 yourself. In your case you could pick Baba Yaga. A real Nictucu would in fact be her sibling.

You can't be sired by the Antedeluvians, but you can finally diablerize them in the Dark Ages setting. This lowers you down to 3rd generation and gives you the Young Third buff.

While playing a Nosferatu, I devoured Absimiliard so that our clan would be free of his spiteful vendetta.

While playing as a Salubri, I diablerized Tremere so that we could take back the power of our clan founder!