Moving a catalog to another catalog

I have three copies of my Lightroom catalog, and I want to combine the two older ones into the newest version. I used the tool to add the catalog and I thought it was going to just add 70 new photos. It ended up adding like a thousand and there were many stacked photos of copies.  When I tried to add the second catalog, I received an "unknown error."  I made sure all three copies were at the latest version and optimized. The other issue preventing me from starting from scratch is that I have some collections. 

 

How can I clean up the stacked/copy photos?  

Can I move the collections to a new catalog?