Portual Trip Trip Itinerary

Lisbon is a small and historic city and the airport is very close. I encourage you to give it a few days. If you aren’t comfortable in cities, hire a guide to show you around and teach you its history. Make sure you try a Pasteis de Nata, delicious custard tarts.
The Belem area of Lisbon has so many wonderful sites to visit. The explorers left for the New Worlds from Belem. Book tickets ahead for the Jeronimos Monastery. We spent nine nights in Lisbon and loved every minute.
I would only give Sintra one night. Personal preference.
Coimbra for two nights is good.
Porto needs at least another night, so make it three nights.
We had a seafood lunch by the beach in Nazare but there is also an upper part of town you could visit to look at surfers. We did not stay overnight there.

So isn't Lisbon mostly up and down steep hills, or are there flat areas?

Baxia is the flat area of Lisbon, and yes, multiple hills for the other neighborhoods. I'd recommend spending the night in Baxia versus an airport hotel. Rossio train station is in the area which is the train station that takes you to Sintra.

Belem is also flat.

Lisbon is "hilly" but that doesn't mean every street is on a hill. There are hilly neighborhoods, but also much of the city is flat or mostly flat. It's also a beautiful city, and - honestly - under-appreciated by most casual international tourists. This is a good thing: it isn't as jammed as the big, most famous European capitals, but has more charm than you would expect.

Every place on your list has hills (and cobblestones, also something to watch out for, for those with mobility challenges). Portugal has a LOT of steep terrain.

Also worth noting: You have a lot of "two night stands" which means you get just one full day in those places.

Looks like your trip ends in the Azores. Lots of hills (and cobblestones) there, too. As much as I adore the Azores, your trip is pretty short to try and squeeze in all your mainland stops AND 4 nights on São Miguel, as well. You will be moving pretty fast; have you considered saving the Azores for a separate trip when you can do the islands justice, and slowing down to spend more time in your mainland destinations?

RIcki, use public transportation e.g. trolleys to get up some of the hills in Lisbon.

I'm counting 13 nights. I also am in my 70’s and I would never plan a trip with so many one and two night stays. All you will be doing is traveling from place to place and not slowing down to enjoy your time here.
Stay in Baixa area of Lisbon for 3 - 4 nights. You can easily and cheaply take Uber up the hills. And, as mentioned there are some hidden elevators and open escalators to ascent and descend hills. The Baixa area and main parts of Belem are flat.
Coimbra is a nice stop between Lisbon and Porto. There are some flat areas, but it also has hills. Be sure to drive out to Conimbriga while there. It’s a Roman town with some great intact mosaic floors.
If you have a car, Alcobaça and Batalha are very interesting and not far from Nazare. Be aware, the giant waves generally don’t start until November. And, it’s not a simple thing to see them as many people all congregate when the big waves are there.
Porto and the Douro are lovely. But, again, you will be dealing with hills. I recommend taking the train to the Douro as the roads are narrow and winding.
Skip the Azores this time. You simply don’t have enough time to do them justice.

Lastly, don’t worry too much about the hills. I live here and do just fine. I try to find flatter areas and take public transport when the hills are too much for me. Do what you can and don’t stress too much about what you can’t do.

Have you been to Lisbon? If not, why skip it.

For the Douro Valley, we did a wonderful river cruise for a week on the Douro, it was amazing. If you don't want to do that take the train up the valley (rails are on the north side of the river) to Regua and see this wonderful valley. In my opinion, it is the most scenic river valley in Europe.

For Porto, consider booking at The In Patio Guesthouse, the best BnB EVER. Book early it only has five rooms.

Hello,

Nice day trips, i would one reduce the 2 days in Coimbra to 1 because you can see it all on the same day and increase the days on the Douro that is spectacular.

Enjoy :)