I was always under the assumption that guests joined at Vaan's level + 2-5?
5 being our 2handed sword person, and 2 being the shorter guest.
I can't remember for the dual wielding. However I believe all of them are relative based off Vaan's level. If not, then off party average.
However,
32(vaan), 32, 25, 24, 31, 25
And the short guest joined at level 34.
Anyway, off subtopic from Emindra.
Quickenings can easily win battles early on. However many people do not have access to these, and it just seems a pretty cheap way to win, merely in my opinion.
Dark gives you area based damage, while if you need levels, there is a save crystal I believe.
Status effects may help you as well. Guess and Test.