Yazidism is an ancient faith, with a rich oral tradition that integrates some Islamic beliefs with elements of Zoroastrianism, the ancient Persian religion, and Mithraism, a mystery religion originating in the Eastern Mediterranean.
This combining of various belief systems, known religiously as syncretism, was what part of what branded them as heretics among Muslims.This is how the Yazidis deal with the "charge" of "syncretism":
[T]hey have a rich spiritual tradition that they contend is the world’s oldest. They were the first people to be created in the Garden of Eden, which they claim is a large area centered in what is now known as Lalish in Iraq. ... During and after a great flood around 4000 BCE, the Yezidis dispersed to many countries in Africa and Asia, including India, Afghanistan, Armenia, and Morocco. Returning from their adoptive countries around 2000 BCE the Yezidis played an important role in the development of the Assyrian, Babylonian and Jewish civilizations of the Middle East. Ultimately, the Yezidis amalgamated elements of all these civilizations into Yezidism, including certain features of the Zoroastrian religion of Persia and some from Islamic Sufism, which were integrated into the Yezidi culture by the great 11th century reformer and Sufi Master, Sheik Adi.A central figure to the Yazidi faith is Melek Taus. The Yazidis are or arguably are monotheistic in that they claim to worship the One True God of the Universe. So who is Melek Taus and what is his relationship to God? As this link explains:
The Yezidis do not believe that the Peacock Angel is the Supreme God. The Supreme God created him as an emanation at the beginning of time. He was brought into manifestation in order to give the invisible, transcendental Supreme God a vehicle with which to create and administer the universe. Tawsi Melek is thus a tangible, denser form of the infinite Supreme God. In order to assist Tawsi Melek in this important role, the Supreme Creator also created six other Great Angels, who were, like the Peacock Angel, emanations of the Supreme God and not separate from him. When recounting the creation of all Seven Great Angels, the Yezidis often summarize the emanation process as follows:Tawsi Melek almost sounds like the Arian Jesus. The first born of creation from the beginning of time to help create and administer the universe. What does the "beginning of time" mean? Semi-Arians like perhaps Samuel Clarke (if I understand the doctrine right) believe Jesus is not created but eternally derived and subordinated to the Father, the One True God, which Jesus is not, but is in some way uniquely specially connected to.
Tawsi Melek was the first to emerge from the Light of God in the form of a seven-rayed rainbow, which is a form he still today continues to manifest within to them (usually as a rainbow around the Sun). But the Yezidis also claim that Tawsi Melek and the six Great Angels are collectively the seven colors of the rainbow. Therefore, the six Great Angels were originally part of Tawsi Melek, the primal rainbow emanation, who bifurcated to become the rainbow’s seven colors, which are collectively the Seven Great Angels. Of the seven colors produced from the primal rainbow, Tawsi Melek became associated with the color blue, because this is the color of the sky and the heavens, which is the source of all colors.
Tawsi Melek was, therefore, both the first form of the Supreme God and one of the Seven Great Angels, which is a cosmic heptad mentioned within many religious traditions. The Jews, Christians, Persian, Egyptians all have their seven angels and creators. ...
While I can't speak to the "Seven" of the other religions, I know of Christianity's. The Book of Revelation speaks multiple times of the "the seven spirits of God." In fact, this led one eccentric "Christian" theologian, Monica Dennington to hold God is a Heptagon (as opposed to a Trinity). Indeed it's arguable whether the Yazidis believe 1. God is a Heptagon or 2. whether and how those special seven are separate and derived from the One True God (analogously, the difference between Trinitarianism and Arianism).
Likewise with the Hindu doctrine of the Trinity. The "orthodox" theology of the Hindus, as we have seen, is monotheistic in that it, according to natural theology which drove the American Founding, believes in the One True God of the Universe. According to John Adams, Hindu theology teaches at the beginning of time this One split into Three (similar to the Christian doctrine of the Trinity). Yazidi theology holds something similar, but instead of Three, Seven (and could cite the Christian Bible in support of the Seven).
Again, natural religion is ecumenical. It posits man's reason unassisted by special revelation can determine the existence of one overruling Providence and a future state of rewards and punishments. And, as it were, that all world religions, following reason, believe in such. Beyond that, the different world religions differ on the details, such as how the True One God becomes Three or Seven or how and whether the divine intermediaries beyond the One relate to the One in Their nature(s) and essence(s).