Hi Iwan,
Yes you have right, Andaluz is just a Spanish dialect, but it is not an easy one, specially on the countryside. But the children learns proper Spanish in the schools and from TV, which means that it’s sometimes more easy to speak with them than with their parents.
I think it is a very good idea to do the research in September - October. This is a main tourist area and the high season ends when the Spanish schools starts after the 15th of September. This means that all companies and authorities works as normal again, the prices for accommodation, food and many other things are falling. The roads are not so crowded and you do not have to watch up so much for UK tourists, who look in the wrong direction when they are crossing the streets.
Don’t hesitate to contact me directly when it’s time for your visit or if you need information. Maybe we could bee seen and have a pint or two.
Best regards from the sunny side of Europe,