@rav kaufman
first of all yannai was the son of the one who enslaved them (although according to abaye, yannai was yochanan, but it seems rava was right that yannai (yonasan) was the son of yochanan who enslaved them).
About him being Cohen Gadol, he was halachically pasul for kehuna because his mother was captured during the wars. This was the reason why Yochanan Cohen Gadol became a tzadoki after so many years (after finding out that the rabbis paseled his wife and kids). Yehuda Aristobulus, his first son, died after the first yom kippur, and then Yannai took over and spilled the water on his feet, got pelted by esrogim and crucified the rabbis. Eventually, he realized he was wrong and sold the kehuna gedolah to Martha bas baythus who gave it to her 2nd husband, Yehoshua ben gamla who restored Torah.
** – i actually have a perutah from Yannai which says on it in old hebrew “Yehonasan hakohen hagadol vchaver hayehudim”