Complex sentence: Thereafter, the Inner Mongols under his son Ejei Khan surrendered to the Qing and was given the title of Prince (Qin Wang, 親王), and Inner Mongolian nobility became closely tied to the Qing royal family and intermarried with them extensively.
Split into simpler sentences: Thereafter, the Inner Mongols under his son Ejei Khan surrendered to the Qing and he was given the title of Prince (Qin Wang, 親王). The Inner Mongolian nobility now became closely tied to the Qing royal family and intermarried with them extensively.