Is it possible for an ummati to surpass Nabi (Sallallahu Alaihi Wasallam) in a'maal?

Q: One day I heard my cousin telling my mother that he heard people in the Masjid saying that the Deobandis believe that it is possible for an ummati to surpass our Nabi (Sallallahu Alaihi Wasallam) in practical deeds (amal). Is this true? If not, how should we reply to such people who are misguiding the innocent people and creating doubts in their hearts and minds?

Kaffarah for breaking an oath

Q: One of my friends is addicted to smoking. His father caught him many times. Yesterday his father caught him and he forced him to take an oath on Qur'an. He said "I will not do this thing again" and having his hand on Quran . He is 17 years old . He said I dont know how long my life is. If I break that Oath, what is the Kaffarah? Is there any way to revert it?

Taking a second wife

Q: I have two questions to ask A) If a muslim husband if found to have had illegal sex with a christian woman as he fell in love with her, can his wife permit and support the woman to change her religion to islam and marry him? B)A wife wants to do sterility surgery in order to stop delivery as she has 3 little kids. But her husband did not permit her to do so. After that the husband chooses a second wife and abstains from sex with the first wife so that they wont have kids anymore. Whats the ruling regarding such a case in Islam?