Joao and Joana were great hosts. They responded very quickly when we had questions. The flat is in Graca and it is a wonderful area to explore with very beautiful views of Lisbon. It isn't far to the more tourist saturated areas, but it is much quieter at night than staying in the thick of things, believe me, we've stayed in Alfama and Barrio Alto, both of which are very loud at night.
The best parts for me of J&J's place is the cleanliness, the comfort of the beds, the historical character of the flat, the heaters in each room!, the metal shutters that shut out the light and cold each night, and the kitchen which felt very clean, nicely kitted out, and had a long, clean granite countertop. My mother, me, my spouse, and our two kids (21 months and 3.5 years old) stayed in the flat. We found the bathroom to be in all quite wet and we had to swap out two of the stools around the kitchen table for straight backed chairs because the kids kept falling off of them onto the hard floor, but other than those inconveniences, it was a dream flat for us all. It felt designed for the conveniences of visiting tourists. Something between a hotel and the usual self-catering airbnb--a good thing!
P.S. If you're visiting Lisbon in winter, bring slippers, no matter which flat you chose...