Conditions for the validity of Nikaah

Q: Apart from divorce, if a married girl escapes and gets married without registration, what are the rules of Islam?

Q: If a man and woman love each other but don't engage in haraam, both are Muslim, believe in Allah Ta'ala, the prophets, Quraan as Allah's book etc. but don't pray BUT know it is obligatory, will their nikaah be valid? Will their nikaah be void?

As I have heard that such couples nikaah is not valid if they don't pray before marriage, don't pray up until marriage and after marriage.

Q: One of my colleagues converted to Islam but she is married to a Christian, and her husband did not agree to convert. So since her husband did not agree to convert, after how many months is she able to get married again to a Muslim man?

Q: Is it permissible to agree not to marry a second or third wife as a condition of a nikaah with the first wife? Is there evidence from the first 3 generations of Muslims (may Allah send peace and blessings on them) of such a condition taking place?

Q: I am 60+ and a widower. My children are abroad. I want to marry a Muslim lady widow to take care of me.

Can I marry her with the following terms:

1. She will get paid an agreed amount monthly, live with me and do all my chores for an agreed period of time, say 7-10 years.

2. She will not get any share in my property after me.

Q: I am a practising Muslim woman and I want to ask if I can marry a Muslim agnostic man. He lives by sunni school of thought, had a Muslim upbringing, is a Muslim on paper and doesn't indulge in anything haraam. He however, is struggling with the knowledge of Allah Ta'ala. He doesn't deny His existence but he says that he hasn't found a proof of Him as well. We both want to marry each other but I want to know if our nikaah will be valid or not?

Note: Agnosticism is different from Atheism and I hope that I made his beliefs clear.

Q:

1. Person A tells person B, “I will appoint a wakeel on behalf of you who will marry you to me”. Person A agrees. Later the wakeel marries person A with person B in presence of two witnesses. Is the marriage valid?

2. Amatullah comes to know that Zaid married her with Abdullah in presence of two witnesses. But she did not appoint Zaid as her wakeel. Hearing this, Amatullah did not say a word but accepted the marriage in her heart and started treating Abdullah as her husband. Is the marriage valid between them?

Q: Islam tells us to marry when a boy or girl becomes mature, age 12-13. But according to science, if a girl marries at 12-13 and becomes pregnant then she has to face problems like losing the new born baby, decrease in her growth of height, sugar problems, high BP, etc .

So in these cases, can we delay the marriage till the girl or boy is 19 years?

In previous days, in the 18th century and before that, did it also happen that they used to marry young and these problems had taken place (decrease in height, high BP, high sugar, risk of death, etc.).

Q: Zaid conducted the marriage of Zainab to Shuaib. But Zainab did not appoint Zaid as wakeel. However Zainab heard the ijab and qubool through the phone and then later when she was asked whether she accepted the nikaah with Shuaib, she said that she accepted. However, she did not notice what was the amount of mahr which was mentioned. So she has no idea about how much mahr she is going to get. Is the marriage valid?

Q: I got married a year ago. Nikaah and everything took place but I never sign the certificate or recieve a certificate saying that I'm married. Am I married and how do I go about for faskh if I don't have a certificate?