Identical v Fraternal

Ok, is it always that if they share a placenta the twins will be identical? And how do they determine when they'll deliver the twins via c-section? I know I've asked questions like these multiple times but my brain is like mush right now haha. I'm having mono/Di twins and was told they will be identical. Don't know if that's always the case? I've tried to google it but I don't get much information