Hah! I managed to beat them on my 3th try! It was pretty close, though. I discovered that "Phys Atk Down" works on them. And even though it only effects 2 of their moves (normal attack and shockwave), those 2 moves are some of their most used moves. With this advantage, I also dammaged them both about equally instead of focusing on just one of them since, when there's just one left, that one starts using its powerful ether attacks more often, which NOT are effected by "Phys Atk Down". So, after killing the first I only needed about 2 more hits to finish off the second one too.

Anyways... now it's time to enter the Song of Nephelin!