Guide recommendations from Lisbon to Sintra

I haven’t used them, but try Lisbon Riders. I have read good things here on the forum.

We had a wonderful guide who is a former teacher, very knowledgeable, and very nice personality. We met her in Sintra and ended in Caiscais, but she can probably come to Lisbon too. Her name is Ana Lucia ‭+351 935 154 224‬. Sintra is full of guides of all sorts, and its really necessary to plan that trip out.

We used Jose from Lisbon on wheels as our private guide.
He took us to National Palace. Quinta de Regalaira, the Moorish Castle and Pena Palace over 10 1/2 hours based on our requests. He obtained the tickets for us so we didn’t have to stand in line to buy them.I would higly recommend him .

We used Lisbon Riders and would highly recommend. Max of 8 people but we had 7. Great but long day.

Another recommendation for Lisbon Riders. I did this tour in March, and it was nice not to worry about the transportation logistics.

https://lisbonriders.com/group-tours/sintra-cascais/

This is what I wrote about the tour in my trip report:

This is another tour I debated taking. Do I take the tour? Do I see
Sintra and Cascais on my own? The more I read about some of the issues
with the buses in Sintra, I thought it would be easier to just take
the tour. Plus, the stop at Cabo da Roca looked like a nice photo
stop. What a great decision, because this tour was just fantastic!!!!
Tania was the tour guide, and it’s too bad they can’t clone her and
have her do all tours. She was warm, engaging, and informative. Plus,
the tour members (8 total including me) were just a great group to
spend the day with. This tour was part guided, with free time in both
Sintra and Cascais.

https://community.ricksteves.com/travel-forum/trip-reports/solo-in-lisbon-portugal-my-trip-report

Several years ago we toured for several days with Pedro of Lisbon and Beyond. The company is based in Lisbon and they do tours in that area, including Sintra.
https://www.lisbonbeyond.pt/home.html