SPANISH REGISTRATION (Seville)

I am hoping you can give me some advice or, at least, point me in the right direction for an answer.

My wife and I are both UK citizens living in France. My wife is also a Spanish citizen via the Law of Remembrance but has never lived in Spain. She has a Spanish passport with an ID number. We are thinking about moving to Spain on a permanent basis in 18 months’ time when my wife receives her UK pension and has a S1 form. Please, can you give us some advice on the registration requirements for residency, health etc. for each of us and also what the requirements are for me to apply for Spanish citizenship as her spouse. Thanks in advance.