in Kasumis case H+K is a unholdable move and causes an unholdable stun. 4H+K is holdable but causes a unholdable stun, so they cannot hold the next move.
no 4H+K can be held lol. the next move after it cant. She has a few moves she can do after it like 3P or 4H+k
no H+K cant be held. and the next move cant be held either. if they try to hold H+K they will sidestep.