Satan and the fallen angels were created as eternal beings. That is why there is a need for an everlasting fire as a place for them in the end. The sinners will also transform like Satan at the second resurrection and will have their place at the lake of fire as mentioned in Revelation.
No, the angels are not eternal. They were created. They were created to serve the House of God (including the sons of God). The rebellious angels will be destroyed in the lake of fire along with those whose names are not in the Book of Life.