I sugguest you need to use the SL avatars for poser (downlaod from sl website). That has the correct number of joints that are possible to pose in SL.
You will see that there is only one joint for the hand so finger poses have to be done with the sl upload setting (point, fist, open hand etc)or by using an SL "internal animation". Similarly there is only one posable joint for the whole head so you have to use the SL "internal animations" for facial expressions or the animation upload setting.
As for the arm movements. I think that is due to the 4 default stands for avatars interferring (again see "internal animations" on sl scripting website).
I hope that helps
-Zarni