We stayed in this airbnb apartment with 2 couples and absolutely loved it. There were two bedrooms and 2 baths, one was not ensuite but that did not bother us. The hostess was great and we found the location convenient but out of the masses of tourists. It is on the upper most floor which allows an amazing rooftop terrace with great views but does come with several flights of stairs (4-5) to reach the apartment.
https://www.airbnb.com/rooms/2322785?euid=31b3aaaf-8c92-8507-b1bd-9f39a64094fb&sug=51
There are no unsafe places to stay in Venice so don't worry about that. When you are reading reviews just remember that most of these older buildings do not have elevators retrofitted so any apartment above ground level will most likely have stairs. If that is an issue for anyone in your party it is better to find a hotel.