Could I say 'My sister and I used to get away with'? Almost. You have to add a bit more. 'My sister and I used to get away with a lot' or 'My sister and I used to get away with a lot of things" or 'My sister and I used to get away with a lot of mischief" or 'My sister and I used to get away with trouble all the time", etc, etc.

No, because that sentence has no object. You need to say WHAT you got away with. For example, "My sister and I used to get away with stealing from the cookie jar" or "My sister and I used to steal from the cookie jar and we always got away with it". "Get away with something" is a good expression, by the way. Very useful and natural!

Thank you, Charlotte! Your comment's helped me a lot!

Hi Diego. When we use the phrase: 'to get away with' in this context, it is meaning: 'to succeed in doing something bad or wrong without being punished or criticized.' We need to add more information to the end of the sentence to ensure that it is clear what that 'something' was. Here are some examples of how you could do this: 1) My sister and I used to get away with sneaking out of the house when we were teenagers. 2) My sister and I used to get away with, not doing our homework. 3) My sister and I used to get away with eating a lot of ice cream, without putting on weight. These are just some examples of how you could use this phrase. Hope this helps you. :)