To be honest I think it's fairly unreasonable to expect them not to park outside their own house and the argument that you can SEE the van through the window is pretty weak to be honest. Just ignore it if I were you, it's really no big deal in the great scheme of things and I doubt you'll get anything done about it no matter how much you spend, who you complain to etc, so since it's really not a hanging offence I'd let it slide.