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?

Ill treatment from one's sister

Q: I am a lecturer. My sister couldn't qualify her studies. Her issue is anger. This makes her life difficult. She is unmarried and 37 years old. She considers me to be responsible for her studies and marriage. She didn't allow me to get married. She broke things and hit me and abuses me. My mother is old and she cries when this happens. What should I do?