Household --> King Candidate?

Is it possible for someone who is a household member to become a King Candidate? Not at the same time of course. Losing your Household in order to gain a Djinn.

This is kind of a tough question to answer as there is no canon precedent. For the sake of not being too limiting though, I'll say a household member can become a king candidate. But yes, doing so would mean forfeiting your household vessel's powers.

In canon we do see KCs who serve other who serve other KCs in the Ren family. Kouen's brothers both had djinn but clearly saw him as their king. Yet, neither of them were his household members despite being his closest allies.

So I think it's safe to say that being a KC means you can't be a household.