Going backwards, Tanzafio is Fantasio's uncle, although I'm not sure if that's Zanta's dad or a mutual uncle. He's the one who supposedly died in Zanta's first appearance, anyhow. I assume the whole family just got an attack of the Raving Clevers.
There's a lot I liked in Aux Sources du Z, even if it does break my brain. But I could see it being a "one-shot" rather than canon. We'll see when the next team starts. Having three Spirous in-universe would be interesting if they were willing to follow up on it.
Finally, I can see that with Zanta as dictator, but he seemed to get more and more competent as time went by. The fact that he even became a dictator in the first place is pretty impressive, given he started as a petty con man.