To make sure that they get along, use skinks of a similar size and species. Enclosures can have several females, but males will tend to compete with one another. As a result it's best to give new skinks a trial run to see if they get along with the other skinks before moving them in permanently.
The difference is that a skylight filter is a basic colour correction filter with a slight magenta tint which has a similar effect on skies as a UV filter (which cuts out part of the spectrum), which is neutral coloured.
Using a Skylight filter is a pretty silly thing to do these days. On some cameras you will be worst off, as some have an external white-balance sensor (the Olympus E-5 for example) which won't see your filter and won't be able to correct for it.