I want to synchonize more than two Calibre directories with more than 10 directories

I tried to synchronize my different Calibre with each of about 10GB files. Copying one into another produce sometimes Chaos and most books in file do not appear in Calbre.
Now I bought 1 TB in Dropbox and will try that in all Pcs Laptops etc.

But really I am missing the option to compare one with another. Also it looks like that its becomes worse, if you have open calibre potable at the same time

????