"I'm having a coffee with them in the office."
Duolingo, please be more flexible with the word order. There's no reason to force canonical order on people, as in this case, where it sounds a bit unnatural to translate the "with them" where it's "我和他們." That would make it translate to something more like this: "I and they drank coffee at the office," or something of the like.
Also, "辦公室" would be a better word for office here, unless we mean something like "at their firm," at which point "公司" would be fine.