rigidbody explain

If I have a Rigidbody on the top most parent object, and then add a rigidbody to a child of its child, will this cause problems in the engine ? Should this be avoided completely, and if so How do I work around this ?

You would work around this by adding the rigidbody onto the object you are selecting and freeze the rotation and position on the x, y, and z.
Hopefully this helped you in some way^^