Marco and Susana were incredibly helpful and the neighborhood is great, I would definitely stay with them again. If you decide to stay here, a few tips that you can't necessarily tell from the listing:
First, the apartment itself is cozy / very tiny. If you are traveling with someone else, it will feel like you are on top of each other all the time. But if you are out and about much of the time, that wouldn't be much of a problem.
Second, the bed is decently large for two, but it really takes up the entire bedroom, it is actually quite hard to maneuver around it. Also the wooden slats in the frame do creak substantially, so this could be a problem if one of you is a light sleeper. That said, the couch in the living room is very comfortable to sleep on if needed.
Third, the apartment was very humid the whole time I was there (late October), it is difficult to get much air flow going. So if you do laundry, it will take days and days for everything to line dry inside, though do note there is a self-service laundry just a block away where you can easily dry clothes for a few Euros.
Lastly, the apartment is on a private street near the top of the Graca neighborhood, so it is typically very quiet with little to no traffic. The Tram 28 is close by but it often packed full with tourists, so I would not count on that to get around. The green line subway is about a 10 minute (downhill) walk away. Getting back up the steep hills can be an ordeal, so the cheap Ubers are very good option, though they can get confused by the address and private road so will often have to drop you off a block or two away.