It’s hard to explain and even harder to learn how to choose between imperfect and simple past. When you’re describing a sequence of events or actions set in the past in a straightforward way, the simple past is the usual choice.
- João entrou e fechou a porta. (John walked in and closed the door.)
For an indirect narration of character thoughts, if the character is 1) thinking about something that already occurred, the simple past or the past perfect are likely to be used. If the character is 2) thinking about something happening at that moment, the imperfect is preferred.
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João viu uma grande desordem em casa. Quem fez/tinha feito aquilo? (João saw a big mess at home. Who did/had done that?) - First case
-
Entretanto, alguém bateu à porta. Quem estava ali? (Meanwhile, someone knocked at the door. Who was there?) - Second case
If the thoughts are expressed in the first person, the above doesn’t apply.
To indicate a location or describe the current state/condition of someone or something (physically, emotionally, etc.), the imperfect is also a better option, especially if “pushed” by verbs such as estar.
- Os móveis estavam fora do lugar e o chão estava sujo. João ficou chocado. (The furniture was out of place and the floor was dirty. John was shocked.)
To indicate habitual past actions/events, the imperfect is also the tense of choice.
- João arrumava sempre tudo e trancava a porta depois de sair da sua casa. (João always cleaned everything up and locked the door after leaving his house.)
^ These are just some examples. Feel free to ask about specific situations that I may have missed! Also, as you guessed, família (family) has a plural sense, but it’s a singular noun, so we treat it as such 
(I’ll check out the new section later)