Just like with pretty much any reptile, you have to get it to gain your trust. You're going to have to keep in mind that they view you as a predator and reacting the way they do is what keeps them alive in the wild. I'm also pretty sure they're wild caught since no one really breeds them in captivity.
For starters, I'd move the tank up to a higher level if you can. Eye level with the skinks would be best. This way you don't appear as a large predator hovering over them. Let them get use to you while you work around in their enclosure without bothering or touching them. After a few days you can attempt to shoe them onto your hand for brief periods in the tank. If you can avoid grabbing them and let them walk onto your hand. After a while of repeating this they will learn that you are nothing to fear and hopfully they will tolerate you holding them for a time. Don't stress them out too much either. A few minutes a day is fine. Most skink species excluding BTS are nervous, shy animals.
Come to think of it, one of my hermits is extremely shy and won't come out at all unless the otheris out.
