Bringing one's wife onto Deen

Q: I am about to get married in few days. The girl who is going to be my wife (In shaa allah) doesn't follow Islamic dressing and hijab. I did talk to her about this in front of her mehram, she says she'll follow it once it comes from her own heart and it shouldn't be forced upon her.I know this will be a sensitive matter after our wedding as she might think that i am forcing hijab on her. So please guide me, after my marriage how do i make her dress in islamic way without forcing it upon her as forcing is forbidden in islam. 

Distortions in the previous books

Q: My question is more of a request for an explanation. I got into a... Lets say debate with a non Muslim and I've answered almost every answer correctly. His one question was if in the Quran it says Allahs word will never change. And if the Bible and Psalms are god's words, why do we say it's changed? The ayah he gave was this one.

The word of thy Lord doth find its fulfilment in truth and in justice: None can change His words: for He is the one who heareth and knoweth all. Surah 6:115

I found another ayah where Allah says:

And recite, [O Muhammad], what has been revealed to you of the Book of your Lord. There is no changer of His words, from Surah Kahf.

I told him whatever God has revealed to Muhammad (sallallahu alaihi wasallam) will never be changed. But he wants to know about ayah 6:115. He says I'm changing the subject and wants to know exactly where in the Quran it says the the Torah and Injeel have been changed.

Using neighbours WiFi

Q: I'm 15. I live in a house where there is no WiFi connection. I had requested my parents to get a WiFi connection. But they refused as they worried it might harm me. A few months ago, I asked for a neighbor's WiFi and they gave me their password. Will it be halal for me to use that? Please keep in mind that I only use the WiFi for educational and Islamic purposes. 

Doubts regarding one's Imaan

Q: I suffer from doubts regarding many things. I am constantly remembering jokes and statements I made in the past that may have been statements of kufr. I have recently read about people singing certain songs that may have taken them out of the fold of Islam. Alhamdulillah I do not listen to music anymore. However I remember listening to and singing the same songs many years ago. I did not know the meaning of these songs at the time. I am now doubting the validity of my nikah and legitimacy of my children due to my actions prior to and after nikah. Is my nikah valid if I have commited these actions prior to nikah?

Woman wearing jeans and short shirts at home

Q: Can Muslim women wear jeans at home? I live with my parents. Whenever I go out I usually wear an abbaya but at home I usually wear jeans with sometimes short shirts. Is this also considered imitating men? I mean there is alot of difference in men's and women's shirts.

So is wearing these kind of shirts with jeans at home also haraam? Many women nowadays wear jeans so is this also considered imitating men?