It’s ‘for’ or ‘at’, not ‘in’. Get your prepositions straight.
I'm American and in is ok here not completely unheard of.
I put "with" and feel it should have been accepted. ב readily takes on this translation in many situations.
"In" is fine in South African English too. No need to be rude about people's English just because you come from a different English-speaking culture.
Nevertheless, if "for" or "at" are accepted in other cultures, they should be as acceptable here. Sure, no one shall be demerited for this choice
"He works for his grandfather's company" still not accepted. Reported!
how do you say 'nepotism' in hebrew?
So, you've never heard of family business?