Tax advice

Your husband will be registering on the EU Citizens Register.  The number on that will be his NIE.  As he will be employed he will just need to prove that thus will not need to prove sufficient income nor medical cover. 

As you will also become resident you too will need to register.  You will be covered re income and medical on your husbands employment situation

My wife, has been in spain 12  years, has no income thus we make a joint tax return.  She was never required to register with AEAT (tax authority)

It is 30 years ago for me but I notified inland revenue (HMRC) that I was from then taxable in spain.  They sent some paperwork which I took to AEAT.  Since then bank interest, premium bond winnings, etc  have been tax free in. U.K. but taxable in spain

Incidentally whilst you will pay the tax in U.K. on the property you let there, you will also need to inform the AEAT as there maybe a top up tax to pay   NB that is not double taxation

NB. All other income worldwide (in your circumstances) is taxable only in spain


Hete is a little ‘light’ reading on the DTA between U.K. and Spain

https://assets.publishing.service.gov.u … _force.pdf

Piskitio
The 183 day rule is just one which established tax residency. 
https://www.blevinsfranks.com/news/arti … -and-taxes

QUOTE
The Spanish tax residence rules

You are resident for tax purposes in Spain if ANY OF THE following apply:

1) You spend more than 183 days in Spain cumulatively in a calendar year, whether or not you are formally registered. Temporary or sporadic absences are ignored for the purpose of this rule unless you can prove you are habitually resident in another country for over 183 days.

2) Your “centre of economic interests” is in Spain– i.e. the base for your economic or professional activities is in Spain. If you earn more income or have more assets here than in any other single country, Spain will be deemed the centre of economic activity,

3) Your “centre of vital interests” is in Spain – i.e. your spouse lives here and/or your dependent minor children. In this case you are presumed Spanish resident, even if you spend less than 183 days here, unless you can prove otherwise.

There is no split-year treatment in Spain; you are either resident or non-resident for the whole fiscal year.

It can be possible to fulfil the domestic tax residency rules of two different countries (i.e. Spain and UK). In that case, the double taxation agreement will set out a list of ‘tie-breaker’ rules to establish in which country the individual should be paying taxes, as it cannot be both. These look at criteria like the location of the permanent home, centre of vital interests and habitual abode. If these do not determine residence it comes down to nationality (or mutual agreement if a national of neither country).