I'm not quite sure exactly what the situation is. If you have a Mac connected to iCloud, and if its Photos' "Settings>iCloud" has "Download Originals" checked,

then that Mac's Photo Library already has all the pictures. If you copy that Library to another Mac, then it will also have all the pictures. The Photos Library is normally located in the Pictures folder.
It's OK to have two different Photos Libraries on a Mac. You can double click on the one you want to use. You can also use "File>Import" to grab the pictures from another Library. If you do have two Libraries, only one can connect to iCloud-- that Library is the System Library. You may have to designate the chosen Library as the System Library by going to Photos' Settings>General:

Here, "Use as your System Library" is grayed out, because it already is my System Library.
Does this address your question? Let us know…