We got the back wheels jacked up and they are moving. like you can shake them and they aren't suppose to be moving at all. The front are steady as a rock but the rear feels like a baby teeth is about to fall off out. What is the cause of this?

 

I guess for starters, do you have any wheel spacers on?
And are you 100% sure all the lug nuts are properly on?

 

If the wheels have been properly torqued on, the next component to check would be wheel bearings.