We plan on arriving in Lisbon (from Seville) on April 30th and flying back home from Porto on May 7th. My wife and I have been to Lisbon (Sintra) for a few nights in the past as well as a day stop on a cruise in Porto. We have no issues again with staying in these two cities but we are looking for recomendations/suggestions - do we split our time 3 nights in each and stop overnight in Coimbra (we will be taking the train). BTW on our leg from Seville we will be stopping briefly ( 3 hours) in Evora.
If you have previously visited Lisbon and Porto, a stop in Coimbra would be nice. It’s is a lovely town and quite different from the big cities. Go Walks does a great walking tour that takes you to the highlights, including the university (spectacular).
Obidos is a small town with ancient Roman walls
Batilha Cathedral is impressive.
Navarre is a nice ocean side city with beach.
thank you kathrynj for the tip about gowalks.....
You do not mention your interests, so this advice is generic.
In my opinion, after many visits to Lisbon, one week there is not enough. If you are interested in the local culture, and enjoy variety, there is much to see and do in Lisbon, and in many day trips out of the city. Coimbra is also nice, and you could spend an interesting week in Porto and nearby places on day trips.