I can only help with the Lisbon and Sintra portion. Whether or not to take a daytrip from Lisbon depends on your interests. Also, what time will you arrive in Lisbon? Don't forget that you need a day to get over jetlag. So your arrival day might not be too productive. So, what are your interests?
We spent 5 nights in Lisbon and that included a day trip to Sintra. So we basically had 3 full days in Lisbon and the day to Sintra. I wish we had an extra day in Lisbon. It's a wonderful city that is very interesting to explore. It's very enjoyable to explore the neighborhoods and sit at miradouros (viewpionts) with a drink to enjoy the views. We spent a lot of time at the Gulbenkian Museum, which is fascinating. Spent a day in the Alfama neighborhood, first visiting the Sao Jorge Castle and then exploring the Alfama neighborhood and then the Mosteiro De Sao Vicente De Fora. We spent a day in Belem at the Jeronimos Monastery, The Discoveries Monument, and the Coach Museum. We didn't have time for the Tile Museum, and I would have liked more time to wander through neighborhoods.
So, if it were me, I wouldn't do the daytrip to Fatima while in Lisbon. Don't forget that 4 nights gives you 3 full days, and I personally think you need those 3 days for Lisbon. Perhaps you could visit Fatima on the way from Sintra to Porto? Check to see if the train goes there. Or perhaps you could hire a private driver for the day if you don't want to rent a car.
You are wise to spend a night or two in Sintra. I think that's better than visiting Sintra as a daytrip.