Maximum period of nifaas

Q: I have a few doubts regarding a woman's impurity after child delivery. I request you to please provide all answers with references so that I can educate my wife and other dependent ladies at my home

1. Exactly how long does a woman remain impure after child delivery? There is an old woman's saying that 40 days is the minimum period. If a woman's bleeding stops after 7 days, but she has irregular bleeding every alternate day or once in 3 days, what will the period be?

2. After the impurity period, can she do everything like praying, reading Quran and physical relationship with her husband?

3. Does she have to make up for the missed prayers during her impurity?