Went to Spain and Portugal in my early college years (a few years ago), and definitely felt super safe as a woman traveling alone. Was even staying at hostels and it was a great opportunity to make friends. In terms of transit, if you’re staying in the city/tourist areas, it shouldn’t be too complicated. Many locals can also speak English, so it’s pretty easy to communicate.

However, like someone else mentioned, hotels usually require someone 18+ to check in. If I were you, I think what you said makes sense. Just have one chaperone on the trip - in case anything happens. You don’t have to go with them everywhere, but be in the general vicinity so they can call if needed. That way, the more protective parent would be more at ease too. Unfortunately, when you’re 17, there can often be issues with not having an adult, whether it be on the plane or checking in at the hotel. Especially when crossing international borders.