Since Yoshihisa did not have a son, he selected Hisayasu, Yoshihiro's oldest son to be his successor, arranging to have him marry his third daughter, Kameju, and adopting him; however; Hisayasu died young, and Yoshihisa had Kameju remarry, this time to Hisayasu's younger brother, Tadatsune, and made him succesor by order of Hideyoshi.
ちなみに義久には男児が無かったため、義弘の嫡男・久保に3女・亀寿を娶わせ養子とすることで後継者と定めていたが、久保が早世したため秀吉の命により久保の弟・島津忠恒に亀寿を再嫁させて後継者とした。