Thanks for asking this excellent question. I have always loved this verse, and so thinking about it is a joy. You truly have a gift, as asking questions is the first qualification for a Bible teacher.
It certainly seems (from a literal reading1) to be multiple thrones. Also, Revelation 4:4 speaks of "twenty-four thrones", mentioned again in ch.11. And Matthew 19:28 (and the parallel passage in Luke 22:30) adds further light on the subject:
So Jesus said to them, “Assuredly I say to you, that in the regeneration, when the Son of Man sits on the throne of His glory, you who have followed Me will also sit on twelve thrones, judging the twelve tribes of Israel."
There are clearly many thrones in Heaven.
But, then we read in Isaiah (quoted again by Stephen in Acts 7):
Heaven is My throne, And earth is My footstool. [Is 66:1]
Does the Father need a physical throne? I should think not, except that the Lord has sat down on that throne.
Complicating this even more, is the Lord's prayer in John 17:21:
... that they all may be one, as You, Father, are in Me, and I in You; that they also may be one in Us...
So in the truest sense, the Father has all heaven for a throne, and we will all be IN Him, when we are finally "one" and God is "all in all" [1Cor 15:28].
So are we agreed that there is one throne, two thrones, and many thrones, and that Heaven itself is a throne?
I really hope this doesn't just come across as cheeky. I am not imagining that this is really an answer, for all of these things have symbolic meanings that even the best scholars of eschatology don't agree on. But I doubt anyone can truly imagine what the throne (thrones) of Heaven will be like, let alone give a truly simple answer to this simple but wondrous question.
1 I am not a literalist in the strict sense.