Not joining the jamaat Salaah

Q: This weekend I was out musafir for a few days with a few friends. We came to a masjid to perform salaah. Two friends we finished making wuduh and the third was still making wuduh so the two of us decided to start our farad thinking the 3rd brother will join us. Our first rakat was almost finished when the third brother finished his wudu. The brother didn't join us but performed his salah on his own. When asked why he didn't join us he said because we didn't wait for him. Is this brother sinful for doing that?

Wet dream

Q:

1) With the regard to your answer that the mani of women is yellowish and mazi is white. If a woman have a wet dream and she find white discharge that means this is mazi and don't need ghusl?

2) Sometimes I have very scary dream and I wake up with big shock but very sure there is no desire or pleasure so this is also count as wet dream?

3) If a woman does not have any wet dream but she find wetness how she can identify that this is sexual discharge or not?

Wet dream

Q:

1) If I have a wet dream but I am sure that discharge is mazi not mani, ghusl is waajib on me?

2) According to your answer if discharge is yellowish then it is mani and white discharge is mazi?

3) If I remember only that I saw a guy in my dream and not remember any erotic activity and find wetness then it does need ghusl or not?

3.1) In this situation if I have discharge, sometimes its white (like normal vaginal discharge) and sometimes its colourless discharge, does it require ghusl or not?

Communicating via one's sister before marriage

Q: A girl is engaged to a guy, her nikaah will be after few months. The guy's sister is close friend of the girl. So is there anything wrong if the girl asks her friend who is the guy's sister to convey him some deeni demands that she has from her future husband? (like the girl wants her husband to get involved in work of tableegh and wear Islamic dresses and few other demands). Similarly, is there anything wrong if she put forth these demands to her future husband via his sister?