My brother-in-law asked me to smoke a joint with him infront of my sister and his grandaughter(10 months old). I said no, then he said he was just joking and had some legal hemp he was gonna have me try? Weird?

Tell anyone who will listen. He is testing you to see if you will tell. He may do something worse next.

Have you ever watched "To Catch A Predator?" Chris Hansen hasn't done all he could with that. He could be using it more to educate young people and their parents. Have you noticed how many predators show up with beer or something else they know the kids parents wouldn't like? There is a reason for that. First of all, predators do that to see if the kids will tell on something they can back out of before they molest the kid. That is one reason. The second is that if they can get the kid to do something forbidden, the kid is going to feel shame and not want to be caught. Therefore they aren't likely to report to the parent what the predator has done so that they won't have to report what they themselves did. Most kids don't stop to think that what the predator did was a jail level offense and what they did was a grounding level offense. They just don't want to get caught.

Tell your parents now, before he does something more serious. If they don't listen, tell the police or someone else who will take you seriously. Yes, your family may be mad at you, but that is better than being molested, or seeing your sister molested. He is waiting to see which one of you tells, and the one who doesn't will be his victim.