Hi! Just sharing from experience — for a group of 8 adults in Sintra, using tuk-tuks works really well.
Most tuk-tuks seat 6 people max, so for 8 people, you would normally have two tuk-tuks traveling together. It actually makes the experience even more fun — you can chat between stops, take great group photos, and stay flexible with your schedule.
We had a fantastic day with a company called Yes, You Deserve! https://www.yesyoudeserve.tours
They arranged two electric tuk-tuks for our group, the guides were wonderful, and everything was smooth from start to finish.
If you want a private, flexible way to explore Sintra without worrying about logistics, I highly recommend looking into a tuk-tuk tour!
Enjoy your trip — Sintra is truly magical!