PhAT Kinematic Issue in branching skeleton

So, I have a kind of pants I made for simplification of this issue. The skeleton or armature is shown in the first image.I want the hips to be kinematic and the legs simulated, so I bring it on UE4 and I do the rigid bodies like shown in the second image (I didn’t make all the rigid bodies) and set the hip ones in kinematic and the leg ones on simulated as shown in the second image.But when I press the simulate button, the rigid body (or bodies) on the left side change the position as shown in the third image.

How can I solve it?
If I do the same with only one leg it doesn’t happen.

Thanks in advance.