No, there is no need to have written consent from your relatives. If you really want to buy a property in Turkey - you can do it without anybody’s permission. You do not need consent from relatives or your spouse to buy any property you have chosen, a villa or a penthouse or an apartment.
Buying a property in Turkey without consent from your spouse is legal. You have nothing to risk. If you change your mind to move to Turkey or your family do not support your with this idea, you will anyway make a good investment. Property prices in Turkey are constantly growing. You can profitably resell the purchased housing or rent it out, earning good money.