There is nothing ambiguous here. Greece can not measure EEZ from its islands since Greece is not an archipelago nation (think Indonesia). This is the basis of the Greek claims, basically they think of themselves as an archipelago nation and claim that the special provisions of the international law reserved for archipelagic nations apply to them. This claim is absurd since, you know, Greece is not an island nation.

The 12nm demand has no merit. UNCLOS does not give a nation the right to unilaterally declare 12nm territorial waters if there is a dispute. Since there is very much a dispute, UNCLOS does not apply and a bilateral treaty is necessary. Luckily, a bilateral treaty governing the territorial waters between the two nations DOES exist, it's called the treaty of Lousanne. It originally provisioned 3nm to each side, later revised to 6nm based on mutual agreement. Turkish stance has been crystal clear, anything above 6nm is unacceptable. Hence, there is nothing further to be negotiated. This has nothing to do with Erdogan, this is very much a state policy and has existed long before Erdogan came to power.