Can you hold a domicile certificate in two states?

The short answer is no. What that means in practice, why it matters at a recruitment check, and how to move your domicile to Uttar Pradesh properly.

In short

No. Domicile is a claim to be a permanent resident of one state, so holding two certificates is treated as a contradiction rather than a bonus. Surrender the earlier one before applying in Uttar Pradesh.

One state at a time

Domicile is a claim to be a permanent resident of one state, and the benefits attached to it (state quota seats, state recruitment) assume exactly that. Holding two certificates is not a bonus; it is a contradiction, and it is treated as one.

What happens if you do

The risk is not usually at the application stage, where states cannot see each other's records. It is at a verification check later (a recruitment board, a scholarship audit) where a second certificate surfaces and the claim it supported is withdrawn. That can mean a lost seat or a lost post, years after the fact.

The clean way to move. Surrender the earlier certificate to the authority that issued it, then apply in UP on the residence or marriage ground that applies to you. Declare the earlier certificate on the UP application rather than leaving the field blank.

Family members in different states

This part is fine. Different members of a family can be domiciled in different states if they genuinely reside there: a sibling working in another state does not affect your UP claim, and their certificate is not evidence against yours.