That depends on the situation. Your brother's sister-in-law could be your wife or the wife of one of your other siblings. As long as the sister-in-law is not married, there is no reason you can't.
It is not okay to date your half niece. You are still in some way blood related and if you ever were to have a child together, it may be subject to deformities.
There are no laws about dating.
No, he's tecnically your unckle just by the marrage of your father and stepmother.
That depends on whether you're ok with them dating. Talk to your best friend about it and tell her if you're ok with it or not.
There are no laws about dating.
This depends on the laws of your area. There are no laws that say it's inappropriate for anyone of any age to date. However, there are laws that forbid sexual activities with minors under a certain age. Check with your states "Age of Consent" laws.
There are no laws about age and dating. The laws involve sexual activity. While the age of 16 is safe in most countries and states, there are others where it is higher.
It is legal to date, there are no laws about what age you have to be to date in any state. There are laws about sexual activity depending on the state. In most places you have to be at least 16 to consent, if not 17 or 18.
OF COURSE IT IS! Why not? Really it is not a crime. There are no laws regarding dating just regarding sex so it's fine as long as the minor's parents are OK with it.
No dating is not illegal as long as your parents are OK with it. There are no laws for dating, just for sex.
Yes, there are no dating laws - it's up to the parents though.
no it will just casue problems between you and your friend. my sister is going through that right now