zahavasdad,
I think you are thinking of his son-in-law (I don’t believe he had any sons). The son-in-law became Rebbe in the late 30s, but during the War many of the Chasidim turned their backs on him when he started advocating that everyone leave Hungary and get to Eretz Yisrael (or the US). The Rebbetzin of the Minchas Elazar disagreed with this and many of the chassidim followed her. The son-in-law then obtained visas escaped with his family leaving the large bulk of his chasidim behind. After the war he stepped down from position as Munkatcher Rebbe but eventually one of his sons took back up the mantle.