Thunderous dou is pretty easy as long as you stay out of the Kirin's lightning. I bet you'll be able to do it by yourself as long as you use a fire weapon.
LOL! Thunderous Duo is 2 Khezu's.
And it's easy. Use a fire weapon and have High Grade Earplug, oh and Hot Drinks with loads of Stamina stuff too.
A SUPER-SHORT Walkthrough:
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Hit his legs, when he's on the floor, attack his neck/head, if you can't, get his tail. When he's doing his electric thing around his body, wait, theb as soon as he's finished go for a run and slash then quickly roll away just incase he does it again. If he's charging an electric ball DO NOT stay under him, otherwise he squshes you when he releases it and it's annoying. Get his wings or tail.
Ahhh, I felt like it. Oh and did you know that in dual fights, the monsters' HP (health) are both the same, BUT, both HP added together is the same as just ONE monster in the same rank quest (that's why single monsters are harder and that'z why it's faster for me to do dual fights).
Hope I helped