Conditions for the validity of Nikaah

Q: I married a Christian girl and conducted the Nikah myself - i.e. I got two non-Muslim witnesses, asked her if she accepted my proposal based on the Mahr I gave her, she accepted and I then read the Nikah Khutbah, and confirmed that I have accepted her as well in my Nikaah. First Question: Is my Nikaah Valid? Secondly - things did not work out and I have subsequently given her 3 Talaaqs telling her that I divorce her in front of two Muslim male witnesses. If she reverts from Christianity - can I remarry her (perform Nikah again) or not? (Does she first need to remarry someone else etc.)

Q: The girl I like was non Muslim. Now she is a Muslim. We both like each other for 4 years. Her parents are not Muslim they don't agree to the marriage and they dislike that she became a Muslim. Does she require her parents permission for marriage?

Q: If a man is to get married but his parents don't agree with the marriage. Is it halal to publicise and go ahead with the marriage without their approval?

Q: I had a question about marrying a second wife? I told my wife I wanted to marry another wife and she said I would need to divorce her first? She would not accept that second marriage! What is the ruling on this?

Q: I am a sixteen year old boy. Can I perform nikaah to a sixteen year old girl?

Q: I loved a girl since one year and she also loves me but the problem is that she is of Hindu religion and I want to make nikaah to her. Can I do so without the interference of her parents?

Q: I would like to know is it permissible that on a daughter's nikaah, her father and brother may be the witness (Gawah)?

Q: My question is on the validity of Nikaah. Is the nikaah valid by mere confession between a boy and a girl that they accept each other as husband and wife? without any supplication or dua ?and without anybody's permission? And also what will be the kaffara if they are doing so?

Q: My question regarding my husband's second marriage? Although Islam gave permission for that. But what if wife doesn't him to do that act?