I do think it kinda works better if he’s trying to put them at odds with one another rather than join together. Only one can become “all the Sith” by inheriting his spirit. Especially because Rey’s vision can only possibly show Daisy on the throne, not along with Kylo. Even though they refer to such a thing in the original film, no such footage exists.

So it’s probably best to stick with the idea that only the strongest bloodline can take the throne. How exactly Palpatine’s dialogue could convey that in this scene without spoiling Rey’s heritage early is possibly worth considering.