You are right: neighbours' son: "ihr Sohn", their car: "ihr Auto", their daughter: "ihre Tochter", their daughters: "ihre Töchter", their sons: "ihre Söhne", their cars: "ihre Autos". It could also be her son, her car, her daughter and so on. To our new neighbour I could say: "Herr Becker, Ihr (formal your) Sohn und Ihre Tochter kommen."
The interesting thing is that "I am her daughter" and "I am your daughter" sound the same (ihre or Ihre). So in real life this will have to be inferred from context(may be even that might not help to a third person, some other form of the pronoun "your" or "her" might have to be used to make things explicitly known).