"Her sons are in college."
Translation:Hendes sønner læser på universitetet.
First of all, we don't really have colleges here. We just have universities, and you can't live on campus.
There are several ways of saying this:
Hendes sønner læser på universitetet. (are studying)
Hendes sønner går på universitetet. (are attending)
Hendes sønner studerer på universitetet. (are studying)
If I were to ask someone about what they are studying (we don't really have majors and minors), I would ask: Hvad læser du?