Need some advice from married people about approaching a woman

Hello!

There's this girl, a woman actually, who I can't get out of my head. She's pretty, funny, smart and has a cocky attitude, but not the annoying cocky attitude, the charming cocky attitude. This woman is 6 - 7 years older than me (I'm 20) but I feel she belongs to me. It feels like she's my soulmate and I want to spend the rest of my life with her. But the problem is this, she's the sister of my brother's wife. It just feels... wrong. Imagine a doubledate where the men are brothers and the women are sisters. It just sounds wierd.
I really like this woman and I'm starting to believe that she likes me as well. I have caught her looking at me a few times and I can tell she's really interested in me and wants to know me a little better. Maybe she was just looking at my big ears or my big nose wondering why in the hell they're so big. I hope it's not the latter. Even though I'm only 20 years and have a lot to learn but I really want to be with this woman, I truly want to marry her!

I'm no bum and she knows it. I worked an entire year at a factory after I graduated from high school and managed to save enough money to buy a real good looking car. After I worked at the factory I decided it was time to study because, well... working at a factory sucks even though I made 18 dollars an hour not counting the nightshifts which added a couple more bucks. So now I study criminology at the university in the same city where she lives. I want this woman! She knows that I have a good future ahead of me and she knows how kind and sweet I can be. She's a really tough chick and I just love that! She's the perfect match for me. She's really beautiful as well. How do I approach this woman?