The scene root does what it says on the tin. It is the root of the model, if it moves the model moves.

To attach seperate models which do not have a skin modifier at the top of their stack you should use the schematic view. To do this:

-Right click on the name of the viewport you are looking in (so if you are looking at your model from the left right click on the word "left") Now go down to views> schematic> new.

-Here there will be a list of bones and meshes. Click on the mesh you want to attach and then press the connecting icon (just look at the buttons, they make it fairly obvious)

-Click and hold on the mesh you want and drag to the bone you want. This should create a connecting line between the two.

-If you want to get back out of the schematic view right click on the words "schematic view" and go to views > left (or whatever view you were looking at)

Regards,

Sundjata