No point in saying something should be done if you have no idea what. I'm the same as you - very frustrated with them, but telling them to not use their Royal titles has failed - they just take no notice as they know the RF have no comeback. IF the RF tried to sue, remove their titles or even tried to get parliament to remove them from the LOS then all hell would be let loose - the racism accusation would be thrown again.
I'm afraid I can see no way out only to grin and bear it until the twunts burn themselves slowly but surely a bit at a time. Their popularity is waning - the celebrities are steering clear of them, any friends they had are distancing themselves. It will take time but, if they carry on as they are doing, more and more people are seeing them for what they actually are - attention seeking, money grabbing frauds, and they will bring about their own downfall in due course.
Just a little suggestion which worked for me ..... get a hobby, concentrate on that but keep an eye on the Gruesomes and have a good laugh at their escapades but DO NOT get bothered by them. Treat them like you would a long running soap program because that is all that they are.