question about who was related to who and how

Hello, I really enjoyed this film. It was fantastic as I'm sure everyone here agrees.

I am just a bit confused because as the opening was so fast-paced and due to background noise in my house I didn't quite understand who everybody was, and how they were related. Obviously I got all the Verma family, but I was still unsure about the following:

1.the man with the moustache who was talking at the party? how was he related to Lalit's family
2.australian 'idiot' - son of the man with the moustache?
3.the girl who was having the thing with the australian - i totally missed how she fit into the picture. i'm assuming she was a cousin or something.
4. the child abusing man. is his wife definitely Lalit's sister?

i would be really grateful if someone could clarify these - obviously i'd watch it over again myself but i don't have the dvd yet.

thanks!!