Where is this stated? I read that Jesus sat with his father in HIS throne, and that those who overcome will sit with Jesus in HIS throne.
Rev 3:21 To him that overcometh will I grant to sit with me in (on) my throne, even as I also overcame, and am set down with my Father in (on) his throne.
Heb 1:3, 8:1, 10:12, 12:2, Mar 16:19, Eph 1:20......is set down at the right hand of God's throne.
He sets upon His throne of glory (Mat 19:28, 25:31) and we beheld His glory, the glory as of the only begotten of the Father, full of grace and truth. (Joh 1:14)
...water of life...proceeding from the throne of God and of the Lamb. (Rev 22:1)(definite article + kia + definite article = two distinct clauses. (Mat 2:14, Joseph took the child, Joseph took the child's mother. Mat 4:8, Satan showed Jesus the kingdoms of this world, Satan showed Jesus their glory. Many other examples. Rev 22:1 John was shown the throne of God, John was shown the throne of the Lamb))
The story of the Pharaoh and Joseph explains well the two thrones. Pharaoh kept his throne, but gave Joseph his own throne.