ancestors? whose ancestors? so they are dead already? How did they communicate with and teach you when they are already dead?
Anyone who is in God is alive though he may be dead to this world. For God is ever alive.
How do you know that God made those men holy? What does sanctified mean?
They have loved each other and all men including their ennemies to the end.
They have when necessary chosen death rather than dishonesty, malice, and all other ways they were pushed by the world to betray life, love, and truth.
They were/are strong in love. They would rather die than kill to preserve their temporal lives. They never killed, and if they did, they repented of it in no ambigous manner. They promoted truth and truth only, never justifying any lie or falsehood. Full faith in the truth is true faith to me. It is sanctifying faith.
'Sanctified' means empowered to love to the end no matter what. To keep the commandments, to respect the holy name of God, human life and dignity, and creation always. Empowerment to endure in the truth and resist all falsehood.
Who are these people? are they priests? or popes? because I've heard and read many horror stories about priests and popes which contradict what you wrote above.
These people are people who have lived and died in peace with God. Even when they committed horrors, they did not try to justify them, but have repented of them and made peace with God. See Psalm 51 for an example of repentance. They are people from all categories including priests and popes. Holiness does not shine from horrible lives, but from righteous lives, from virtue, true repentance, love of all men.
What does single heart and single mind mean?
It means no contradiction of conflict in heart or mind or both. Moreover, true faith comes from them when they speak from one heart and with one mind. The Church is one as God is one.
Don't christians worship a 3 persons God? Is that integrity?
By three persons you mean: Father, Son, Holy Spirit ?
If yes, how is that not integrity?