Factors that make Qurbaani waajib

Q: I have heard sveral conflicting views on the following. What is the Shafi'ee mathab on Qurbaani? Who is it waajib on? Should it be made annually or once in a life time? Can one qurbaani be made on behalf of a family?

Q: If a parent has money invested for his baaligh child, but the child will only get this when he turns 18, is qurbani wajib upon the child? (e.g. Eduction policy)

Q: A person purchased an animal for qurbaani. Before the day of qurbaani, the animal got lost. After purchasing the second animal, the first animal was found. Which of the two animals should he slaughter?

Q: Is qurbaani waajib on the father on behalf of his minor children?

Q: Will the waajib qurbaani be valid if it is carried out on behalf of another person without his consent?

Q: What is the shar’ee ruling regarding a person who took a vow that if a certain work is accomplished, he will perform qurbaani? Will there be any difference in the ruling between a rich or poor person?

Q: If a poor person upon whom qurbaani was not waajib purchased an animal with the intention of qurbaani, will qurbaani become waajib upon him?

Q: If I have sufficient money to make one qurbaani during the days of qurbaani, even though that money might not be nisaab amount, will it be waajib for me to make qurbaani?

Q: If a person upon whom qurbaani was not waajib received some money which equals the nisaab amount just before sunset of the 12th of Zul Hijjah, will qurbaani be waajib upon him?

Q: What is the ruling regarding Qurbaani, when a person is performing Haj and his family is offering Qurbaani in his country of residence? And also what is the reason to offer sacrifice of two animals while one is performing the Haj?