Nicole Brown Simpson’s sisters are getting candid about her tumultuous marriage to O.J. Simpson. The slain mother-of-two’s siblings, Tanya, 54, Dominique, 59, and Denise Brown, 66, claimed their family member greatly suffered during her relationship with the NFL star, who passed away in April. “I never knew he inflicted so much pain onto her,” Nicole’s eldest sister alleged of her romance with O.J., which lasted from 1977 when they began dating until they divorced in 1992. “The hitting, the kicking, the punching, the throwing up against walls. ‘You’re stupid, you’re ugly, you’re worthless. Nob…