Are are the level of the pirates from strongest to weakest?

It depends on their battle fleet. Loosely, it’s Mediterranean > Somali > East China. But that can change a bit depending on what you send out after it. If you have like level 5 aircraft but like level 3 fleet support, all your battles will come with similar loses. One carrier group you have could dominate a level 13 East China Pirate, but another of similar level would lose to that pirate. So always click on their fleet details to truly know what you need to beat them.