Indeed zij can mean either she or they, depending on the sentence, but this are two different meanings, similar so the singular you and plural you in English, the verb conjugation will tell you which of the two is meant.
- Hij eet = He eats/He is eating
- Zij eet = She eats/She is eating
- Zij eten = They eat/They are eating
- Zijn vis = His fish
- Haar vis = Her fish
- Hun vis = Their fish
It depends on the word type, the verb zijn = to be, the possessive zijn = his:
- wij zijn hier = we are here
- jullie zijn hier = you are here
- zij zijn hier = they are here
- het is leuk hier te zijn = it is nice to be here
- ik zie zijn fiets = I see his bike
BTW it's better to learn the verb conjugations (ik ben, jij bent, hij is, wij zijn, jullie zijn, zij zijn) than to try to translate word for word, for instance: jij bent = you are, so here zijn = are doesn't work.
Here in Canada we're not consistent either. Dinner can be either lunch or supper depending on who you're talking to and context, but it has the feel of being a more substantial meal. I would be loathe to call just a sandwich "dinner", but a large meal at lunchtime might fit it. As for me, I stick mostly to lunch and supper.
Not most people; maybe in Manchester or Leeds, but in belfast or london dinner is more common. Its really regiinal. Most people dont call trousers 'pants' in Stafford ...but they do in Bolton.
I think dinner might be more correct to the Queen's English... But I totally agree that in Wigan they'd call it tea.
A lot of people are asking this question. It's probably because 'zijn' has two meanings. It's either possessive as in 'zijn avondeten' or a plural verb of to be as in 'wij zijn'. Because of it's plural meaning in the verb, I guess people assume a plural possessive meaning as well, so make sure you get this:
Zijn avondeten = His dinner Wij zijn = We are Hun avondeten = Their dinner
DancingGeek is right. Dutch people would use 'Zijn ze van hem'. Zijn zij zijn sounds very weird to me, but I see where you're coming from. With this approach you could say 'Zijn ze de zijne?' but I suggest you forget that immediately since it's VERY formal and possibly never used.
Note that 'ze' as in 'zijn ze van hem?' is the same thing as 'zij'. So you could also say 'zij zij van hem?, but when those two are interchangeable, always go for 'ze' since that's more overly accepted in Dutch.
I would guess it's mostly about emphasis. In "the fish is his dinner" the fish is in focus. You might ask, "may I eat the fish?" And receive "No, the fish is his dinner." In "his dinner is the fish", the dinner is what is in focus. It might answer a question like "what is he having for dinner?" Technically, they describe the same thing, but the focus is on different elements.