Question: who told doflamingo to kill moria?
Answer: After Kaido has a lot of business with Doflamingo. So it was Kaido has to ask Doflamingo to kill Moria. After Moria is one of the worst enemies of Kaido, or at least it once was. This mean Kaido is much stronger than Sengoku, so Kaido would be crazy powerfull.