All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, we draw your attention that not seeing your father since 1997 is considered as cutting ties with him and being rude to him. So, you have to repent from this act if not seeing him was not due to a sound religious reason. But if this was due to a sound reason like being in another country and not being able to travel, and the like, then we hope that you are not sinful.
As regards the ill-treatment of the wife of your father to your brothers, then you have to advise her in a good manner and with wisdom hoping that Allaah will guide her and rectify her behaviour so that she would treat your brothers kindly.
You may make use, in this regard, of beneficial books and tapes on upbringing. Besides, you may supplicate Allaah to straighten her affairs. If you do so, you will find fruitful results, Allaah willing, especially that you have mentioned that she prays; this implies that she is on much good.
Allaah Knows best.