agent required to register guests with the police

Have you got the Tourist Licence as I understood that as part of this, you gain access to the Guardia Civil register online.

Unless you use a registered agent to handle everything to do with the bookings it will be you who needs to register with Guardia Civil to obtain the online login for your property, and you have to do it in person.  You will need an appointment and take your property's tourist license certificate, your passport and your NIE.  They will take all the details and issue you with your personal login for your property.

If you do not have a tourist license for the property then you can be heavily fined for advertising it as a holiday let and then fined heavily again for having people rent it, (and the renters can also be forcibly removed from the property by the police!)

Technically the form is completed online by you, then printed off for the guest to sign (all guests over 16 years of age need a form completing) as soon as they arrive.  However may not be physically possible for you to do, so you have 2 choices:     1. On arrival of the guests at the house your keyholder logs on using your login details, completes the form with the guests' passport details, prints it off and they sign it (access to internet and printer required at the property).    or    2. the keyholder fills in a paper copy of the blank form (it can be downloaded so numerous blank forms printed off in advance) which is signed on arrival by each guest and then you (or the keyholder) transfers this information to the web site, prints off the form and attaches it to the signed hand completed copy (I have been informed by two legal firms that this second option would be acceptable to the authorities).

You are not supposed to inform the Guardia Civil until the person actually arrives as you can't 'uninform' them if one guest doesn't show.  We have a section on our contract where they enter the passport details so we do have them in advance, but they still need to be cross-checked before the paperwork is signed.  I send a scanned copy of that part of the contract to my keyholder so she can fill in the paper copies of the form ready for signing and I fill in the on line form once she has texted to say the guests have all arrived and the passport details I have are correct.  She gives me the signed copies on my next visit to attach to the completed printed off on-line unsigned form.  

Due to GDPR we do have to tell the guests in advance that we will be sharing their passport details with the keyholder and with the Guardia Civil (it is stated on our booking form and contract as well as on our own web site).  The completed forms must be stored under lock and key due to their sensitive nature.

Thanks for the info but I'm looking for an agent in my area to deal with the forms and be a keyholder.

What happens when family or friends stay at your Villa,

Surely you don’t need all their details as well?

If family are staying and not paying anything at all then you wouldn't need to declare them as they are not renting the property. If they are paying to stay there then they are renting and you would need a license, need to declare the rental (even if a reduced rate) and do the Guardia Civil forms as usual.