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.
Regardless of their strength, skylight filters do not have any effect on the camera exposure, are equal to UV filters in terms of cutting through atmospheric haze and protect your lens against dust, moisture and fingerprints that can all be damaging to lens coatings if not removed in a timely manner.