looking for insider tips: restaurants, cafes, bars...

Ciao Claudia! 
If you want to avoid the touristic places I suggest you some area in the suburb of Rome.
Go to EUR Palasport to discover another side of Rome. It's a "modern" part of the city, it was built during fascist regime and the architecture is really interesting. Dont' miss the Civiltà of Lavoro Palace, Parco Centrale del Lago, Piazza Guglielmo Marconi, Centro Congressi Nuvola Di Fuksas. Recently i had dinner at Ristorante Il Fungo Quattordicesimo Piano, there is an amazing view from there and the food is excellent. It's a bit expensive but i think it's worth trying.
http://www.ristoranteilfungo.it/index.php?lang=en

Something completely different is Monti (Cavour metro station). I suggest you to shopping here, there are a lot of small shops with hand made items. My favourite are Kokoro and Sottobosco. Then have a rest at Zia Rosetta.
http://www.ziarosetta.com/


But you should find time to go also to Garbatella and Quartiere X Ostiense area. By the way, recently I answered a similar question here in Trippy, check it out (https://www.trippy.com/question/Rome-Best-non-touristy-and-authentic-places-to-eat-in-Rome#answerItemView_5398845be4b0ee88a5eb8202)
Write me about your interest, i can give you more suggestions if you need!

A 3 days visit to Rome with your Mom and sister sounds like a great plan!
If you are seeking for something not that "touristic", you might want to check out my startup BonAppetour.
https://www.bonappetour.com/s/Rome
It is a community of local hosts, who are ready to invite you to their home for a nice homemade dinner where you can feel the true Italian hospitality. Or, if you also fancy mastering the art of Italian culinary, you could also take part in some of the cooking classes that the local hosts are offering.
Enjoy!