I am sorry that you have been the target here. It sounds like your parents are just "mad" and venting and you are taking it as "them blaming you". They are probably venting at you, and it is out of "their feeling overwhelmed and confused about how to handle this".

It is "not" fair to you to be the one your parents "vent to". Your parents need "professional help" and that is what your response to them has to be when they "vent at you" like this.

The "only" way this situation can be resolved and dealt with is by your parents getting outside counceling, and your brother also getting counceling as well. This disfunction is showing this need, so my advice is for you to stand tall and when they vent at "you" demand they stop it and get help.

(((Hugs))))