In my demo, the first slide should show the original set of 8, then the second slide should show the 4 selected, and then the third slide should show the 2 selected.
As it is currently set up, the unselected are disabled. I think with this type of triggering, I'd keep those visible so that people can see how they're progressing, rather than hiding them.
Another option, requires more triggers, is to create an object with states for all possible choices. Then when you get to the slide you have to change the state of the object to the first choice, then change the state of the second object to the second choice.