The term Beast in the Bible is revealed in Daniel 7 to be referring to Kingdoms and this is where we need to get our interpretation of what the word Beast means in the Bible and Daniel also refers to them with personal pronouns as well, "he and him".Your claim is false again, (The Beast) & (The False Prophet) are noted in the first person singular throughout Revelation, He, His, Him,
Both The Beast and False Prophet are human men, that will be cast alive into the Lake Of Fire as seen below.
20 And the beast was taken, and with him the false prophet that wrought miracles before him, with which he deceived them that had received the mark of the beast, and them that worshipped his image. These both were cast alive into a lake of fire burning with brimstone.
The beasts are symbolic for Kingdoms under the control of the spirit of antichrist or the the beast from the abyss and being symbolic, your idea that they are in the first person singular doesn't mean that John is speaking of two men.
Furthermore the beast and the false prophet are first and foremost an evil spirit of antichrist that is leading the physical kingdoms of the beast from the sea and the beast from the earth and therefore it is the spirit that is cast into the lake of fire alive and not the bodies plural human bodies that they operate through.
Definition of a Beast= an evil spirit and it's body or kingdoms of human beings through which it operates and does its evil.
Actually there are three Beasts mentioned in Revelation, the beast that rises up from the sea of the nations and then the second who rises up from the earth and which is also called the false prophet and then the beast that rises up from the abyss and which is the King over the other two bodies or kingdoms under his power.