Xkavre,if his previous rejections were on non immigrant visa,like f1 tourist that shouldn't be a prob cuz now u r filing an immigrant visa. Previously be had to show he would come back to Nepal but now quite the opposite he has to prove the relation is genuine and he wants to live with u in the US. Unless he has lied and was blacklisted in the past I dont think it will be a prob. My moms tourist visa was rejected 3 times before we sponsored her and brought her as a pr.