i made new weaponanimations amd made the left hand child of the right hand etc. so the weapon is being grabbed properly all the time. the problem is that now that i want to export the animations i somehow have to either plot the translations made by the parent (right hand) to the child (left hand) or transform the local transformations into global ones so that once the left hand isnt child of the right hand anymore, it still moves the same way.

does anybody has an idea how to do that or ho to solve the problem another way?

Have you tried adding keyframes for the child bone? I don't know much about animation, but if the position of a bone changes in any way you could probably add keyframes for the particular bone and retain that movement.

Without knowing all the details of this would-be animation, instead of parenting you could just create a null outside the to-be-exported hierarchy where it would be located at the weapon position then pose constrain (enable CnsComp first!) both arm effectors to it, then direction constrain both hand bones to the same null, then animate the null and plot the animation to the bones.

its a bit late, but thank you for the replies!
i created a null where the left hand is, made it child of the right hand and contrained the left hands pose to that null.