Companies or people that can handle the whole residency process.

I hope this find you and your family well. I am contacting you looking for some assistance with becoming a resident of Spain. Ours is an unusual scenario with many different factors hence we are contacting you in the hope that you will be able to assist.  

My husband and I are British nationals and holders of British passports, we currently live in Dubai in the UAE but looking to move to the Murcia - Mazzaron - Campasol region in the next few months, definitely before the end of the transition period. The problem is at present while my husband can move to Spain any time from August 4th  however, I will not be able due my employment contract join him in Spain until after December 24th  . 

From our understanding if my husband can obtain residency I can still apply for residency under the old agreement as my husband will have residency. Our questions are as follows:

How long do we have to be in Spain before you can apply for residency, and if indeed can he apply with just a long term rental contract?

We know that there are 2 step from research and being in contact with various organizations and joining online forums and webinars, we are just unsure if we have not left it too late and if indeed it is viable or worthwhile my husband coming to Spain prior to my contract ending December 24 th . 

Can you advise who can start the process of obtaining an NIE number for my husband? Or if there are any companies or a Gestor who can assist in this process, we realize that there is indeed a very tight time frame.

Many thanks