get your drivers to cycle around some of their routes for a different perspective?
Sticker above back left bumper saying 'Cyclists please do not undertake when vehicle turning left' or something similar? Always scares me when people do that.
Stick a mobile phone jammer in them so the driver can't text while the engine is running. (Illegal, unfortunately due to interfering with everyone's signal)
Educate them that all road users have a comparable "right" to be there, that if cyclists can reach out and touch the van when overtaking then they're too close, and that 'road tax' was abolished in the 1930s?
I think that should do it.
If there's any time when one of them is not needed, arrange with either schools or cycle safety groups for people to get a chance to sit in it and see what the visibility is really like - park it up and put bikes in the blind spots...
Make all of them ride a bike in circles around the van whilst one of them drives it slowly eating a pasty, drinking tea and having a row with the wife on the mobile....
inform the drivers that if they recieve one single complaint from either a cyclist or any other road user they are out of the job....
don't give them such a silly schedule of drops... might take the pressure off them and let them relax a little more.

