En mi familia somos cinco personas: mis padres, dos hermanas y yo.
Explanation:
En mi familia somos cinco personas: mis padres, dos hermanas y yo. This means: In my family we are five people: my parents, two sisters and me. "Mis" means "my", but in Spanish it differs when you talk about something in singular or plural. Parents is plural, so the correct possessive adjective is "mis". Option D (mi) would be correct if Francisco was talking about one person instead of both parents. The other options, "tus" y "sus" are both incorrect because they mean "your" and "their", and Francisco is talking about himself and his own family.