@seamus452
Ah, you're married, this is another issue.
I replied to your Green NIE questions in your separate thread/topic. Your EU Citizen Registration Certificate is what you need, and this is your FIRST step.
Your wife (assuming she is not dual citizen with EU passport like you) is done AFTER you are a legal resident (with your Registration Certificate). The process is called "Family Reunification". The guidance is here:
https://www.inclusion.gob.es/web/migrac … pe-hi-102-
This requires a proof of the family relationship (e.g. marriage certificate). Foreign certificates need the Apostille AND (if not in Spanish) a CERTIFIED Spanish translation. The marriage certificate can be Apostilled when you are back in USA. Or you can do a Google search for Apostille USA and find an agency who can get your certificate apostilled. Once it's apostilled, you need to give it to an official Spain-registered translator. It's expensive as you have cost of apostille itself, an agency helping you, an official translator, and multiple courier shipments as the document goes through the different steps. It is, for sure, a Pain in the proverbial.
You'll also find that the address needs a PROOF, unlike for your initial EU Citizen Registration Certificate. You'll almost certainly need an official rental contract (or deed, if you buy a property) and your padron certificate (town hall registration) showing BOTH your names.
This process is necessary for your wife to be a legal resident.
To be clear, this means there are TWO distinct immigration processes that have be done in order. The first, for you, as an EU Citizen. The second, for your wife, as the family member (spouse) of an EU citizen (and Spanish resident). Both steps need you to provide your residence address, but only the 2nd step requires you to have PROOF. Therefore, you also need to formalize your new home in Spain before you do this 2nd step.
After you are BOTH legal residents you can investigate public health insurance / social security contributions, and you can look at the tax residence implications. You can (probably) choose to remain non-tax resident by spending less than 183 days per year in Spain. I suspect your attorney is mentioning the Marriage Certificate/Apostille in reference to the Family Reunification step, not the tax resident / tax paying step.