Praise be to Allah the Lord of the Worlds.
A Muslim should be keen on pleasing Allah the Almighty. He should also forgive others for their mistakes and put the past behind him/her, since Allah the Almighty Says (What means): "Those who spend (of that which Allah hath given them) in ease and in adversity, those who control their wrath and are forgiving toward mankind; Allah loveth the good." {Al-Emraan, 134}.
He Also Says (What means): "And verily whoso is patient and forgiveth - lo! that, verily, is (of) the steadfast heart of things." {Al-Shura, 43}. Our role Model in this regard is Prophet Mohammad (PBUH). Upon the conquest of Mecca, he (PBUH) forgave all those that had offended him since forgiving is a characteristic of the righteous. Therefore, you should fight your ego and train it to forgive and show indulgence so that Allah may forgive you in the Hereafter. He the Almighty Says (What means): "Let them forgive and show indulgence. Yearn ye not that Allah may forgive you ? Allah is Forgiving, Merciful." {An-Nour, 22}.
Nevertheless, if you couldn`t forget what they have done to your mother, then deliver the rights which Allah made obligatory upon you through showing piety and kindness to relatives and in-laws. And Allah the Almighty Knows Best.