Ok , I get everything you are saying and we will sort it out bit by bit.

firstly, Your in charge of yourself , not the BIL , or your parents.
We all grow and separate from our parents , like a puppy becomes a big dog.

Everyone has a designated position in the " Family " like the BIL and you wont change it as people don't like change. This is why they are not listening to you . Even if he did something bad they would cover it up to keep things the same.

Yes , the "Family "would sabotage your romance , why , yes again because of "Change ".

There can be no change in the " Enmeshed Family " you have to be the " Big Dog " here and escape with your man. This is your life , not theirs and they should respect what YOU want.