combine two folders and deleting duplicate files ?

(1) I have two folders "folder 1" and "folder 2" 90% of the content on each folder is the same....both large folders over 100GB. On windows you can copy all contents and paste into the other folder and click rename the file and if there is the same file name it would just rename the file name to file (2), etc. On Mac it will give you give you the options of "keep both" and rename is as "copy", but you can only do this if select 4 or less files, if you select more than 4 files it won't give you the option to keep both.

(2) After I figure out how to merge both folders...how can i delete duplicate files? I'd like to sort it by size and file name so i can confirm they are duplicates. Or if there is a way to delete duplicates in 2 seperate folders than i wouldn't need to merge the folders above.

I think the GUI method has been different for every version of OS X I've seen (which is only 10.4 - 10.9). Thus, there is no single answer without knowing your version of OS X - unless you want to use terminal.

Personally, don't believe I've had the need to either merge folders or delete duplicates in years.
If I did, think I'd download MuCommander - free.
By default, it presents you with 2 tabs both shown simultaneously so that you can open the two folders in question and compare the files side by side.

To delete, either move a file to the trash or right click and select delete.

Here is a sample of my local external and my backup media drive movie folders: