In Garo: Honoo no Kokuin, we see that the golden armor (Garo) can only be passed down to one's lineal descendants (for example, from Anna's father [the former Garo] to Leon and Alfonso).
What about the other armors, like Zoro and Gaia, though? Do they have any restrictions on who can use them? Regarding Zoro, in episode 24, we learn that
Germán's child with Ximena is going to inherit Zoro. That doesn't necessarily mean that Zoro has to be passed lineally, but it does sort of suggest that that might be the case.
On the other hand, it looks like Gaia doesn't have any restrictions based on bloodline, since Raphael was able to pass Gaia onto Alfonso, and I don't see how Raphael could be a lineal ancestor of Alfonso - Raphael is not Alfonso's father (the king), nor his maternal grandfather (the former Garo), nor his paternal grandfather (presumably the previous king, who must be long dead), and anybody from Alfonso's great-grandparents' generation should also be dead.
Answers based on the tokusatsu version are welcome if they make sense in the context of the anime.