"The two brothers went to the hill."
Translation:Los dos hermanos se fueron al monte.
Yes, you can use the non-reflexive fueron as well. It's pretty much like in English, giving the sentence a slightly different focus:
- Fueron al monte. - They went to the hill.
- Se fueron al monte. - They left for the hill.
the proposed translations shows colina. the soltuion in duolingo shows al monte(mountain) - not hill