Surprisingly I beat the lich duo on my first playthrough at level 3 and haven't been able to beat em since :/ (I don't know what strategy I used but it worked)
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Wow you really don't need to do that. Just use Jeanne's barrier on her and she should survive just fine. The wargs are 9x more likely to target Lianna and Jeanne anyway, since they're the ones with the most mp (they literally eat mana).
Whenever you get stuck, just have a good look at your skills and items. I'm sure you can come up with a good solution yourself xD