All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
This man is only obliged to perform one Ghusl (ritual bath), but it is better and desirable for him to perform ablution after each sexual intercourse in order to be more active sexually. It is confirmed that Anas said: "The Prophet used to have sexual intercourse with all his wives performing (only) one Ghusl." [Muslim]
Allaah Knows best.