Conditions for the validity of Nikaah

Q: In Islam, is it halaal to get married under 18 but by Law its illegal to get married under 18?

My question is: Can I do nikah but not get married by Law (I'm under 18 and the girl is under 18 too and we are in Europe... In my country like most of the countries its illegal to get married under 18)

Ma Sha Allah im 17 and she is 16 which means we have to wait 2 years... We both are muslims Ma Sha Allah, and she has a "wali" and everything else. Alhamdulilah its okay but that is the one and only problem.

Q: A girl and a boy used to like each other. One day, one of the friends of the boy asks the girl ‘Do you marry Zayd (the boy)?’ The girl replied ‘Yes’ in front of many people. Are they married now?

Note that the boy did not say anything nor appointed his friend to conduct the marriage. The friend just joked with the girl.

Q: Does a nikah done as a joke (just for the sake of fun) in a friends gathering without the presence of the wali, become valid?

Is it valid when the girl says yes just because of peer pressure of acceptance in a group and without having the knowledge of the sensitivity of this subject/issue of nikah.

Q: My question is regarding my marriage. When I met my husband I wasnt paying much attention to religion so we married in court as civil marriage. My father and mother left me alone in another country so I didn't have any wali present on the day we got married. Now since I learned more about Islam and I am concerned, I would like to know if our marriage is valid?

Q: If a girl says to a man that you are my father in law, does nikah happen between the man’s son and the girl?

Q: If a girl and boy gets married without any witnesses, the nikah is invalid. In this case, does the boy have to divorce the girl or there was no marriage in the first place?

Q: My Muslim friend married a Hindu guy. She also has a baby with him. It's already 4 years but her husband does not want to accept Islam. He is very good and caring. My friend is an orphan. She continues her Namaz and Quran. What must she do?

Q: I am a Muslim guy and I have been in a relationship with a christian girl for a while. I am trying to make this relationship permissible on all aspects and I want to marry her but we are not planning to register this marriage in the court (not legal marriage) just Islamic so that we can be confident that whatever we are doing is not a sin/Haram. We are very serious in this relationship and we want to take it to a legal marriage level but not now since she is still a college student and her parents and not fine with her getting married that early. I believe, I can fulfil all the Islamic marriage requirements from bringing in witnesses to announcing my marriage. It's worth mentioning that we live apart in two different cities, more than 6 hours away from each other but we do see each other every once in a while.

My question is: Is marry this girl according to the Islamic laws permissible?

Q: I'm in love with a girl who is 7 years older than me and she love me as much as I do. We both want to get married and start a life. So to ask her hand for marriage there is one thing I want to know, is it permissible to marry someone older than you like with 7 years age gap? And we both meet each other everyday as she is my teacher and I'm her student, she teaches me. So is it okay?

Q: During my nikah, I was not opposed to the marriage, however the witness only asked me who I wished to take as my representative, not if I accepted the marriage or not. My brother performed the qubool on my behalf. Is this correct, or did I have to verbally say I accepted the marriage?