Can we enter a prenup if my fiance is not a U.S. Citizen?

My fiance is from Sudan and has very little in the way of assets. He is coming to the U.S. to marry me and will be starting over in terms of a career. I have done well financially and am a part-owner in a family business. My family is pressuring me to have him sign a prenup that guarantees he would not get any of our business if we divorce. I love him and want to help him get an education here in the states and have a good career and life. Even if our marriage didn’t work out, I would not want to be unfair to him, but I understand my family’s concerns. If my fiance is willing to sign a prenuptial agreement, would it even be valid if he is signing it when he is not yet a U.S. citizen? Could I even enforce it?