It is hard to see from this angle and so far away, but I would say that it will be easier if your feet are closer together. This is a case where you want your skis to function as a team though still independently. Some things to think about while doing these:
In order for a ski to pivot from under your foot, it needs to be flat. In order for it to be flat, you need to have your bones stacked (ankle, knee and hip inline) over it. You should be able to stand on flat ground on one ski and pivot it (ski will make a bow tie in the snow) without moving forward; just standing still. This will also show you if you are fore or aft. It is hard to do if you are aft. Doing all this on two skis means each ski will be under each ankle, under each knee and hip. Doing this going downhill means your body needs to be perpendicular to the ground and not see level at the pivot.
When you go to pivot, you need to be biased downhill or perpendicular to the ground beneath you. At about second 0:13 you get a side view and your are slightly aft and this is where you need to be slightly forward. This is also why you are pivoting at the tip of your ski and not from the center.
When you slip, it looks like your dropping your hip uphill. I think this is initiating your aft bias. Try more rolling the ankles and less hip (seen at second 0:14).
From second 0:10 on, you can see that you are pivoting around your ski tips. You need to pivot from your feet and not the tip (bow tie).
I'm not sure but it also looks like the hill might have a double fall line (slopes in two directions - down and to the right). That makes it a little more challenging.
So you know, I love this drill and it usually starts my day skiing.
With all that said, you are doing pretty good at it for your first try. Try doing the stationary pivoting of the ski on flat ground and you'll have a better feel of what you need to do on the hill. Remember it comes from the center and not the ends.