I have a snake and the jaw is split. That means I have a right and a left jaw bone. The tongue is parented to the left Jawbone. However, i need the tongue to be parented to the right jawbone as well so when i move both jawbones simultaneously the tongue follows the movement 100%. But when only one moves the position is only 50%.
Blender 2.92.0
I tried it with another bone and copy transform but it didn’t work.
You may thing about restructuring this; building up a single jaw bone which has a left and right child bone and one tongue bone. The question is: why left and right bone inthe first place ? Is this an alien creature with different anatomy?
I wrote that this is a snake. They have jaws like that.
Okay, on that point you win. Forget my second sentence (i thought only disarticulateable jaw). But anyway, maybe a pseudo bone (or even use the name armature here because it is too close to real jaw bones 
) for just unite the following left and right jaw bone of the snake (see ? i learned something 
) and additonally the armature chain of the tongue muscle (and now my eyes hurt of the ongoing twinkling)
+ (
+ (Left-
, Right-, 
)
Ha ha LOL
Easy way to do what you want is an armature constraint. Unparent the tongue root from everything-- it should be root level. Create an armature bone constraint for it. Designate each jaw bone as a bone contributing to the armature constraint, with a weight of 0.5.
Wooo. It works!
