to go back home = to return home in English.
It is the English in question here. Physically, this means returning to a place where a person was previously. "I am going home" (Voy a casa) doesn't give the sense of a round trip that "go back home" and "return home" (vuelven a casa) both relay.
I have the same question.
What I'm wondering is this: Since "They are coming home late" didn't work, but "They are going home late" did, that suggests to me that it's a matter of the speaker's perspective. In my experience, an English speaker who says "They are coming home late" is at or near the home, whereas one who says "They are going home late" is at or near the place "they" are leaving. But would this also be true of Spanish? That is, who would say "Ellos vuelven a casa tarde": a neighbor woken by a drunk couple returning at 4am, or the host of a party who was hoping her guests would be gone earlier?
Volver is defined as "to go to the place you departed from" (def. 20). It doesn't require any certain perspective. If you want to go for a certain perspective, you can use more directive verbs: partir, salir, ir for the party host; venir, llegar for the disgruntled neighbour.
Accepting "They are going home late" but not "They are coming home late" is a little inconsistent. But I'd say that "going home" gives the feeling of "returning home" somewhat better that "coming home".
Ouz, you cannot say "to house" in English. The term "house" refers to a specific building, so you'll mostly use an article or something similar with it: "the house", "my house", "a house", and so on.
The phrase "a casa" refers to a movement with your home as the goal, referring to wherever you live, which is not necessarily a house.