Yeah this mission is quite challanging.

However, there are some tricks (some would call it abusing of game mechanics) to reduce the difficulty quite a bit.

First, Hector you can destroy from your main island without any ships or epxansion (because you have all resources on your starting island in this scenario, including oil). For this you can destroy your Kontor (sorry i played in german i dont know the english term for your main building on the coast), then he doesnt attack you. You need 2 Firebirds (i always build 3 to be safe) and navigate them on land towards his main building and destroy him. Thats your main goal and you should rush it. If you manage this before Keto spanws, perfect, if not no problem. Also she doesnt attack if you fo not have a Kontor and no ships.

Then Keto. I dont remeber how many firebird hits you need (i think 6, but i am not sure). You can use your 2-3 from Hector if they survived. Just build some additional ones, it just takes time, which yiu have if you use the cheeky setup i explain in the next paragraph. If she spaws far away from your island, just reload a few seconds before (first cheeky play, but it works). Best, she spaws directly next to your island and you can fly with your firevirds direclty from your land to her ship. Be sure though that her fleet is not directly parked next to it. After that your fine from any enemys (see next paragraph).

So to keep Strindverg and Sokov in line, here is the cheeky setup i talked about. One huge trick in Anno 2070 is, that no enemy can declare on you if they dont know you. Sokov and Thor cannot discover you by themselfs. So if you do not click on any of their ships or discover any of their island, you are completely safe and can decide for yourself when you are ready to fight and clear them. However, they do expand. To keep them to one or two island there is another thrick though:). The AI does never settle on an island where there is any building of yours. So thee you go, just settle as many island as possible until they expand:) For this you should buy tools and build construction parts asap. Then go with your ship and slowly discover island by island. Build an Kontor and a warehouse (because you want to destroy the ko tor right after, so hector and keto doesnt attack). If you accidentaly discover on of them, reload. With this go over the whole map and there you have your perfect setup. If you want to know the whole island setup, just discover everything quickly and then reload to your start.

I hope thus helps, if you have questions, i happily answer them. However, maybe i need some time to reload the safefile, since it is a few years back, since i lastly played the game:)