Translation:Someone's cat eats a lot at our house.
I would like to know this as well. It should mean that the cat eats a lot of food. Otherwise the "a lot" would need to go at the end. But I have heard Norwegians speaking English get this order wrong pretty often. Maybe it is the same translation in Norwegian and requires context?
Hos is actually the preposition here. Hos here means at the place of. In this case oss or us, but it could be followed by any person. For example, hos bestemor is at the place of grandma or at grandma's place.
This might explain it better. https://www.youtube.com/watch?v=6HVxdV-ItSY
It says it with hos. Hos here means at the place of. You can use it to say you're at any person's place (but only people and not organizations or institutions). So to say "I'm at the doctor's" or "I'm at the doctor's place" you would say "jeg er hos legen."
In this case we're saying the cat is "at the place of us." Or "at our place." So we say "hos oss."