Until a planet is found any speculation is valid as long as they meet the conditions.
According to orbital mechanics and multi-body interaction Planet 9 is supposed to be 5-10 Earth masses. Any number of objects in that "same" "orbit" range is possible as long as the sum of masses is the same. Anymore and there would be an imbalance causing rejections etc. So there could be multiple or a single large planetary system with multiple moons.
According to orbital mechanics and multi-body interaction Planet 9 is supposed to be 5-10 Earth masses. Any number of objects in that "same" "orbit" range is possible as long as the sum of masses is the same. Anymore and there would be an imbalance causing rejections etc. So there could be multiple or a single large planetary system with multiple moons.