Could someone please explain "hjemme" and "hos"?
I'm not really sure of the difference between the two and how to use each.
It is correct that "hjem"is "home" and "hjemme" is "at home". "Hos" is a pronoun from the same lingistic root as "hus" = "house". If you say "Han er hos oss" it would not only mean that "he is with us", but rather something like "He is with us at our house" or "He is at our place". Depending on context it could also mean that he is in another place with us, for instance at the office, but it would be somewhere where we have a kind of ownership, not just anywhere. In this the word "hos" has a slightly different meaning than by, next to or at.
Your example is not quite correct i Nowegean ears, it should be "det er gjester hos oss" = "There are guests with us at our place"or "gjestene er hos oss"="The guests are with us at our place" A common phrase would also be "Gjestene er hjemme hos oss"