Jaak's father was Ado and his mother was Mari. His paternal grandparents were Paap and Anu; his maternal grandparents were Andres and Epp. He had four brothers and six sisters, named Mats, Ado, Jüri, Peep, Liis, Kärt, Eva, Ann, Anu and Tiiu. He had two half-sisters named Mai and Liis.