we got ours at the box office on the day

I agree with Michael K above. We took Uber to Pena Palace, and Uber to Quinta de Regaleira (skipped the Moors Castle only because we were running out of time). We actually got our Uber from Pena Palace to Quinta right outside the Moors Castle. If you exit the castle through the gardens, it’s a short walk uphill to Moors Castle. The reason we did Uber was tuk tuks did not take card—cash only, so be prepared if you want to take the tuk tuks. The bus from the train station does go to all three, if I remember correctly!

Yes tickets required for entry to the grounds. It is interesting and a bit quirky but wouldnt go out of my way with a toddler in tow.

Better to book in their web, particularly if you want a guided visit which I recommend

Sí, hay suficiente espacio en el parque para sentarse y comer provisiones que ha traído con usted.

Penso que o desconto é válido somente para professor local, ou talvez, com carteira e validação internacional. Aqui não tem muito isso na verdade... (meia usualmente é para seniores e estudantis). Nao saberei lhe responder com precisão, peço desculpas.