You can't see it well because of my shirt and the unexpected sunlight, but in both exercises my ribs are tucked the entire time (similar position as a properly executed hollow body hold or dead bug), and I am contracting the muscles in my entire body. Essentially, your body should remain still and rigid, with the arms being the only part that moves. This is a sign of a strong and stable core.
These versions of the exercises are more advanced as my feet are elevated and I'm using a much smaller ball, so start out with your feet on the floor and with a larger ball. Then progress to using a smaller ball and with your feet on the floor, and lastly elevate your feet.