At the ball, what were the actions of Mrs.Bennet, Mr. Bennet, Mary, and Mr.Collings that caused such mortification/embarrassment and what did these actions show about their characters?

The social interactions at the ball provide the reader with a picture of the formalities of early 19th century English society and the extreme importance which rank and wealth played in social relations. Elizabeth is extremely aware of these social conventions, and is continually being embarrassed by her family's lack of propriety. Mr. Collins' introduction of himself to Mr. Darcy as well as his long and pompous speeches combined with her mother's indiscreet conversation about hopes for a marriage between Elizabeth and Bingley and Mary's poor performance skills serve to completely mortify her.

I think these actions show that most of these characters have an agenda. Much of this "agenda" has to do with the procurement of money, title, social status and perhaps (last on the list) "love".