Turkey feels less and less like a European country as the days go by, and public behavior like this should not be tolerated.
If they love their neo-Ottoman sultan so much, they should enjoy the great Peace and Prosperity he built in Turkey proper, including the Glorious and Strong Turkish Lira. Not live among the unbelievers and pay with their dirty Euro.
Membership in Grey Wolves should be considered on par with membership in neo-Nazi structures. No reasonable country would suffer foreign neo-Nazis building structures right under their noses.
But what you say stands out, because there is an easy solution that's not tainted by racism: These people are threatening other people. They form an organization to promote this. We as a society have a tool against that: Law.