Brian McKnight’s son and ex-wife are speaking out in response to the singer referring to his estranged children as “evil,” RadarOnline.com has learned. The Grammy-nominated singer, 54, took to social media to respond to backlash after praising his stepchild Julia McPhee as his “one and only daughter,” despite having a biological yet estranged daughter, Briana McKnight. In a reply to a comment on one of his Instagram posts, Brian wrote that his children were a “product of sin,” and that he “didn’t raise them their mothers did.” He also wrote: “In order to live a life that you love, you have to …