Marrying one's step brother's daughter

Q: I have a step brother (same father, different mother), one of his daughters have been recently widowed. I myself am divorced recently as well. A few people have raised a question about us getting married since my widowed niece is just half niece.

I am clear on the ruling based on Quran (Chapter 4, Ayat 23) that this not allowed.

Can I please request guidance on this please?

Husband preventing wife from taking care of her old mother

Q: What should I do when my mother is old and she has no one to look after her. My husband does not want me to take care my mother. I am the only child. My father passed away.

I told my husband that she does not have anyone to go to but he ruined her visa application so she cannot stay with me. I am sad to see her in pain but I don't know what to do? If I take her side then my husband blames baseless things in her.

What do I do in such a situation? He's not supporting me in this. He's also not a religious man and he does not pray at all. He does not follow Islam. There no family members that can step in and stop him. 

Purchasing a TV on interest

Q: I bought a TV with option of no cost emi of 3 months. After emi completion, Later I found out that it is not permissible and it involves interest as bank gives loan and charges interest and then I checked my statement and found out.

I usually buy items paying all amount but this happened first time that I had to take this option of no cost emi. From the day, I came to know I am feeling bad. Should I sell of my TV or keep it? If I sell I won't even get 50% of amount which I took. So I am in a dilema. What should I do in this case.