They make a foaming wasp spray that expands when it comes into contact with the surface. We use this a lot as it covers over the nest and prevents the wasps from even dropping onto the ground. If your not sure if your hitting the nest or not this may be of some use to you.

In any case, I would suggest that an exterminator come in and correct this issue for you. They use a powder that when it comes into contact with the wasp will kill it. They puff this powder into the holes where your seeing the bees and the powder gets onto all the surfaces within the nesting area. AS the wasps enter the hole and walk to the nest they come into contact with this poison and simply die off.

Treatments are not that expensive and are really worth the expense knowing they have properly removed the bees from the house cavities.