Keep mass when attaching rigidbodies

I have a blueprint containing a rigidbody with simulated physics that has several other components as children.

The physics of the entire object seem to be simulated solely based on the mass of the parent rigidbody. Changing the mass of the children makes no difference.

So I set them to have simulated physics too but that makes the object fall apart.
I attached the objects to the parents in the event graph and selected Weld Simulated Bodies but, again, the children seem to lose their mass. It’s like only the parent has mass.

How can I combine rigidbodies into one without having the individual parts lose mass? I want the different parts of the object to have different weight.