Looking for advise on socializing my ferrets

We are fostering a 4yr male ferret. He has been in his cage most of his life and the only ferret. We had 3 ferrets 1 female, Lucy and 2 males, Loki and Trudeau. Lucy past away last November and Trudeau was diagnosed with insulinoma and lymphoma. So we wanted to get Loki our 6yr m a friend before Trudeaus time. In comes Momo. Hes very scared of our two males, understandable since he was alone his whole life. The thing is now Momo goes after Trudeau and Loki and now they are scared of him. I get they need to dook it out, but now they are constantly running away from him to scared to stand up for themself. We are keeping them separate in the cage and swapping out the blankets each night. Just not sure what else to do. also Loki is twice the size of Momo. I'm surprised hes so scared of him.