What do I do about my little brother failing his class?

So apparently while I m  was away at college my little brother has been failing his CCE Psychology class. My mother has known he s been doing horrible but didn t say a word, and I always had my expectations. Yes borderlined an "F" his first 2 quarters and got a 41 during this quarter! Now she s mad at me because I refuse to talk or help him in any way.

It s clear that he s not doing any homework because all of his classes say he s not doing homework on the report card. Those teachers hadn t failed anyone I knew so I know he s just playing all day.

I honestly feel like there s no point in helping him, and certainly no point in explaining to her that she needs to start getting on his back because she told me "Its ok because he s doing great in his other classes". Which is a lie because he has 1 A, 3 Bs  and 1 C. 

Has anyone had to deal with a situation like this? Help me.