Hotel check in

[Lienite]

Is there any hotel in lanzarote who would let couple both 17 to check in independently? Letter of consent and card details from parents would be present.
Thank you

They need to be 18 and have their own credit card.

I believe it might be hard to find an hotel accepting minors without any adult. Even with letter of consent. I would just send an email to the big chains in Lanzarote Iberostar, Riu, H10, Melia, Barcelo, ...
One more thing, you should consider, if you are lucky they are accepted: Some hotels might require you to present the credit card that has been used for the booking. Any chance you can transfer the trip money to your child's account and they use their card to prevent this issue?

There is a new thing this year with regard to information which Spanish hotels have to collect from visitors and send off to their government - assume this covers Lanzarote - I don't know whether this will have any effect or make it more likely they would want visitors to be 18.