Translation:I'm having coffee with them at work.
公司 means company or firm (as its primary meaning). However in English we rarely say 'I had coffee "at the company" (or "at the firm"). We are more likely to say "at work" or "at the office". Note that this sentence would not be said by a teacher or nurse. They would have coffee at the school, university or hospital. Languages do not have one to one correspondence between words. Also meanings may be broader or narrower in one language than another.
Normal English phrasings aside, isn't the construction "我和他们“ making the combined group the subject of the sentence? In which case it should be translated "They and I/I and they are having coffee at work." Translating "I'm having coffee with them at work" makes the other people into a modifier on the action, not active agents as part of the subject.
As a native English speaker, both are perfectly correct. "I'm having a coffee with..." and "I'm having coffee with...". Both are widely used although the latter is more technically correct. https://www.englishforums.com/English/HavingCoffeeHavingCoffeeCorrect/bwxmnw/post.htm