take them both. i am not aware of losing benefit after cooking coconut oil because it's stable up to high temperatures. NEVER cook with flax or fish oil, though.
the coconut oil is completely different from flax/fish oil, in that it has no omega-3's or essential fatty acids. in fact, it's more then 90 percent saturated fat. do your research. the saturated fats in coconut oil are beneficial to health.