Would probably help if the US stopped selling cluster bombs to the Saudies :
How US Cluster Bombs Banned by Most Countries Ended Up in Yemen | Mother Jones
But then neither of them signed the convention banning cluster bombs so I suppose it all right to manufacture, sell and use them.
But they arent being used against IS in Yemen but against the so called moderate rebels.
Indeed its hard to tell just how much traction IS has in Yemen for there are conflicting reports :
ISIS Fails to Gain Much Traction in Yemen - WSJ
ISIS gaining ground in Yemen - CNNPolitics.com
Whatever, that country is quickly being turned into another Libya with several factions fighting for control.