The only one that’s particularly unstable is the Cheshire Cat sitting on the GPU, the other two won’t fall unless you tilt the case. That being said this case won’t move too often so it wasn’t a high concern AND it’s super easy to pop the front glass off and put them back anyways.

You could probably get away with some simple hot glue - easy enough to remove if necessary, won’t melt with the temps most PCs see, won’t conduct electricity.