You may have to lower your expectations. I've never seen cats play together with a toy. It's always either taking turns or one watching the other. If one is too timid to play while the other is around, then you might have to play with them separately.
Toys with motors (moving ball, floppy fish, etc) have all scared my cats because of the noise.
They did like cork balls though. Something about the texture and weight. And tissue paper, cats love crinkly tissue paper.