Sorry, none of them were legal. This was pure and simple the idea of the Turks being unhappy with Greek Cypriot rule. Source: lived in Cyprus for 5 years.
Wasn't there terror attacks against British and Turkish on the island -not only on Turkish people, Greeks felt like island 'rightfully belonged to them' -? Wasn't there attempts to unite island with Greece at times by the both Greek and Cypriot nationalists ? There was a guaranteering agreement precisely for this reason and Turkey used his rights.
https://en.wikipedia.org/wiki/London-Z%C3%BCrich_Agreements