Experienced Travelers - Itinerary Critique Please

We only spent three hours each in Obidos and in Nazare on our way from Lisbon to Porto. I’d add a day or two in Lisbon.

Not sure why you have so long in Nazaré in the winter unless you are hoping to see the giant waves. These only occur when there are storms in the Atlantic and are infrequent. If you want a beach day, do a day trip from Lisbon to one of the beaches on the Cascais commuter train line.
With twelve days, add more time to Lisbon. I’m not certain how easy it is to use public transport to Obidos. But, as the other poster said, it’s worth a couple of hours.

8 cities in 12 days. You will spend a lot of your time staring at the back of a seat.

Not sure what Nazaré, or any of those places are like in December, off season. Consider stopping off in Óbidos on the way to Nazaré since you need to go right by it. That would save having to double back to see it. An alternative could be to use Tomar as a base to take day trips to Nazaré and Coimbra. To me, unless spending the night in Óbidos it could easily be skipped due to the large numbers of tour groups that clog the main street through town during the day. Other than the old town wall, there’s little to it.

I would echo the comments of others to spend more of your Lisbon time in Lisbon instead of mostly using it as a base for day trips. You could easily fill four full days in Lisbon without ever leaving the city. Not saying your day trips aren't worthy of doing, but I would want at least two (honestly three) uninterrupted days in Lisbon itself. Definitely make sure to hit the Rossio market and see all of the holiday lights downtown in December, it's magical.

I would drop Evora, Nazare and Obidos (none of which I particularly enjoyed). Both Lisbon and Porto have plenty to see and do and a single day in each is definitely not enough. December days are short, so day trips mean coming back in the dark - really wasted time when you could be exploring the places where you're sleeping. One more reason I'd recommend 1 or 2 nights in Sintra and and overnight in Coimbra.

We are going to be in Portugal for eight days at the end of November, starting in Lisbon and ending in Porto. Should we spend time/nights in Coimbra on our way up and if so how much time? And what about Douro Valley? We are 65 and traveling with our mid-30’s kiddos. Thanks!