Blend 2 animations properly

I have an animation of the character walking backwards and two more animations of the player walking right-backwards and left-backwards (not diagonally).
I want to mix the animations two create two new animations of the player walking backwards diagonally. I tried achieving that in the blendspace editor, but it is just unnecessarilly complicated and doesn’t even work properly.
Is there an option to blend 2 animations and create a new one (without a blendspace)?
If not, is there a program that does that?