Agreed that the 8s chain won't work well at all with a 10s cassette, so I'd fix that first.

Unless you're using friction shifters, which isn't likely considering that you have a 10s cassette, a 105 derailleur isn't going to shift well paired with a Campy cassette. Depending on how "old" the campy derailleur is, it may not handle a 10s cassette either. Still, your odds improve dramatically using a Campy derailleur.

I don't recall seeing which brake/shifters you are using - again, you will have much better shifting if you run all Campy. The 11s cassettes are pretty much interchangeable between Campy and Shimano, but 10s was not.