If you wish to stay in Spain for longer than six months of the year, you must register with your local Town Hall, and be placed on the “Padron”.
The “Padron” is simply a registration list, which records everyone living in the local area. It is similar to the electoral roll in the UK. For this you will need your NIE and passports, a copy of your property title deeds, and sometimes an electricity or water bill.
There will often be benefits to registering you family on the “Padron” – such as free or subsidized use of local facilities.