You would have to say "persons," which is the plural - but the plural is rarely used except in legal documents or statements. For example, you might see five people in an elevator, but the sign in the elevator might say "Limit: four persons."
While it is factually true; let's not forget that this is a lesson to teach words and sentence structure. So, it's best to keep the given form. And besides it would be logistically impossible for the database to contain every possible version of every sentence we translate.
Yes, but we usually say "There are four people in my family" instead of "I have four people in my family."
Ditto 12/31/18. Seems to me the latter is the more correct and acceptable American English translation!
Nothing compared to that person with 80 grandchildren.