This is the bit that causes the most problems for foreigners making a will in Turkey because you can't make a will that is outside of the law as set in the Civil Code. Basically the state has decided how your inheritance will be "portioned" and to whom it will go.
Reserved portion law in Turkey
A person is free to make testamentary dispositions in preparation of a will within the limits set by the Civil Code.
Articles 452-453 of the civil Code guarantee a portion of the will as the rights of offspring, father and mother, brother and sister and surviving spouse. According to this,
A) the reserved portion and legal inheritance right of offspring is 75%
B) the reserved portion of inheritance for father and mother is 50%.
C) The legal inheritance right for every brother and sister is 25%.
D) If the surviving spouse shares inheritance in other situations but no with children, the reserved portion is 50% of the legal inheritance right.
E) If the deceased person leaves some wealth to an association which is working for public benefit or to a foundation which has tax exemption, in those cases reserved portions are 2/3 of the amount mentioned above.
Read the full text here
http://insideguidetoturkey.com/the-guide/essential-information/item/576-wills-and-inheritance-in-turkey