Please excuse me for jumping in so late. All the previous suggestions have been great.
Regarding where to stay, we found the VIP Eden aparthotel good value. It is central and within walking distance to sights and transportation.
https://www.viphotels.com/en/Hotels/VIP-Executive-Eden/About-Aparthotel.aspx . Friends just returned from Lisbon and found the Barrio Alto to their liking. They said there were more authentic, reasonably- priced restaurants there then in the core area of town. They found their apartment through Booking.com
I would avoid the restaurants on the pedestrianized street to the right of the Opera House. The meals are of so-so quality at inflated prices. However, if you do find yourself there and wanting to eat, competition for customers is high and you may be able to bargain for a bottle of wine or dessert or something else.
We found many excellent seafood restaurants across the Tagus river in the Cacilhas area. For the price of a bus ticket you get great views of the city from the ferry. It leaves from the Sodre terminal.
I'm assuming your wish to visit Evora is to see the Bone Chapel and perhaps the Roman temple. It's a couple hour bus ride each way. Doable yes but perhaps not worth the time involved.
We found the Monument to the Explorers in Belem worthwhile. There are great views from the top. While there the Jeronimos monastery is just across the way. The Pasteis de Belem pastry shop is a tourist stop for custard tarts. There are better places to get them but this is THE historic bakery. One can take an old trolley out there. However, Tram 28 is the one tourists usually opt for. Hang on to your wallets and handbags!
Best of luck to your sons and safe travels.
Dennis