Alrighty then, lets talk about sharpness.
I'm sure you know all the sharpnesses and their modifiers.
Red = .5
Orange = .75
Yellow = 1.0
Green = 1.125
Blue = 1.25
White = 1.3
Purple (2G) = 1.5
For the first rathalos, all you need is green, but blue would be nice for the extra damage.
As far as a weapon to use, i would use a hammer or longsword, but duals work well too.
For good tactics, its just like any other wyvern, just keep bashing it. If the roar it does when it enters rage is messin you up, jump into IT'S left leg. Why? Cuz, whenever it roars while entering rage, it steps forward with its left leg. If you roll into it you will take some (very small) damage, but it you will not be stunned by the roar, a useful tip.