Should I let my small sister be a 4th wife to a 47 years old man?

Good day mamas and papas in the house, please I need your advice on how to go about this. My younger sister who is just 16 years old is pregnant, I won't lie that when I heard i didn't judge her because I did and I have been sad since because of the shame she brought to our family, a lot of people asked us to terminate the pregnancy for her that she is too young but the man responsible came forward and accepted the pregnancy and he is a very rich man. He has promised to take care of her and pay all her school fees to masters level even she wants. This man is an alhaji and he has 3 wives already and none of them are literate which is what scares me because I ma not sure that he will keep to his word. My mom has accepted that they get married, in fact, their marriage is in December and I just don't feel this is right. My father is late so my mom is in charge and the only she is interested in is the money she would get from this alhaji. Please house, how do you suggest I handle this matter. Should I let my small sister be a 4th wife to a 47 years old man?