Buying a house abroad

We have a second home abroad ourselves. Through that we've got to know a lot of expats from various countries. We have learned quite a bit from those who have made a permanent move.
For example, of those who didn't already have a second home, most of the rest rented before they bought, to make sure their area of choice was right for them all year round. It also helped many realise the importance of decent outdoor space attached to their residence was something they'd under estimated.
Language skills are more important than many expected. Although they might live near other English speakers, it's good to have a few basics for medical, house or administration matters.
Proximity to an airport with direct flights home.
Hope they enjoy their adventure!

Can they speak Spanish? For anything from dealing with Estate Agents, to tradespeople for fixing things that break (plumbing, etc). You'll get english speaking tradespeople, but they'll probably charge you for the convenience.

Also, check how close is it to an airport, and the transport links to said airport. IMO, ignore Ryanair airports, as they have pulled out of airports in the past to move to cheaper airport.