Long term rental

Assuming that you are British (with British passports) ...

You can only visit for 90 days in any rolling 180 - so no more than 3 months in any 6.

As l understand it the NIE will not prevent the 90/180 rule kicking in for UK nationals. You either need a work/study visa (or similar) or have your residencia. Would love to be corrected on this as some of my family a longing to come over and rent for 6 months at a time.

Also, as described elsewhere on this forum, the process of gaining residencia in Spain , for an UK national, is now more convoluted and expensive than before .

No way around it...you would only be able to stay for maximum 90 days in 180 and do this twice a year.

NIE is purely an identification number.