OK. You do seem to have several different locations being searched, which would explain the multiple copies of everything. You should need only one Official library—I'm guessing it's meant to be the …Documents\Lego\ldraw folder. But whichever one you want it to be, that should be set to type Official (not Donors), and you only need the top-level folder. You don't need …\models and …\parts and …\p since LDCad will automatically search for those sub-directories. So those extra entries can be deleted. (But keep the …AppData\Roaming\LDCad\donors entry; that is your actual Donors folder which is used for flexible parts and comes with LDCad.)
Then when you download the parts update, it should go into the folder that you've designated as Official. (If you download the whole library you can just replace the whole thing; if you download only new parts then they have to be added to the existing Official folder.)
Then for snapping to work (assuming it's enabled with shift+P), the library has to be associated with a shadow file—right now you do have that set up with the first entry, but it looks like that folder is only the updated parts that you downloaded, so that's why most of the parts you select won't snap.
So to summarize, you should really have only two entries in this window:
1. Type: Official | Location: your main LDraw library, with any new parts added into this library | Shadow: like you have it set up now
2. Type: Donors | Location: the fourth one in your current list | Shadow: not needed
Then when you download the parts update, it should go into the folder that you've designated as Official. (If you download the whole library you can just replace the whole thing; if you download only new parts then they have to be added to the existing Official folder.)
Then for snapping to work (assuming it's enabled with shift+P), the library has to be associated with a shadow file—right now you do have that set up with the first entry, but it looks like that folder is only the updated parts that you downloaded, so that's why most of the parts you select won't snap.
So to summarize, you should really have only two entries in this window:
1. Type: Official | Location: your main LDraw library, with any new parts added into this library | Shadow: like you have it set up now
2. Type: Donors | Location: the fourth one in your current list | Shadow: not needed