The Avos and their children
Both Avraham and Yitzchak had children who were not their spiritual heirs. Only Yaakov of the Avos had all of his children follow in his footsteps.
I heard the following idea from the Rosh Yeshiva of KBY R' CY Goldvicht to explain this.
Each of the Avos was known for a specific midda.
Avraham passed down to us the midda of chessed. Chessed is giving to others, but unfortunately chessed can be used for aveira purposes as well. Too much chessed is not good either. The arayos are called chessed because the arayos means a person doesn't recognize any boundaries, what is mine is mine and what is your is mine. This is Yishmael who inherited this midda but took the midda of chessed to it's aveira side and was involved in arayos.
Yitzchak passed down to us the midda of gevura. Yitzchak was a gibor in the mode of איזהו גיבור הכובש את יצרו. However, Esav took this midda to it's negative side and was a murderer.
Yaakov Avinu was able to take these 2 middos of chessed and gevura and synthesize them together and be an איש אמת not going too far in any direction. Yaakov's midda was to nullify himself and do what the situation warranted and therefore all of Yaakov's children turned out to be tzaddikim.