Answer
The question of ‘Abdu’l-Bahá's leadership was challenged by his immediate family members, specifically his half-brother, Mírzá Muhammad ‘Alí and his uncle, Mírzá Muhammad-Qulí, due to their own leadership ambitions and disagreements over the interpretation and implementation of Bahá'u'lláh's teachings. They accused ‘Abdu’l-Bahá of deviating from his father's path, leading to a period of conflict and division within the Bahá'í community.