It is hard when you are not in and your family are. I would get upset when I see family photos of them all on holidays having a good time together without me. Now I keep away and try not to know what is going on. Rather, I count myself lucky, as I have many great things that happen in my life.
Rather than comparing yourself to others in your family, concentrate on what you enjoy and are good at. Everyone has strong points. Maybe you never let yourself come to learn what you like and what your skills are. You do not need to look to your parents and siblings for validation, you have your friends and yourself.
You suffer from guilt, the chief tool religions use in manipulation, because of your childhood indoctrination. This is pointless. Get rid of words like sin. Sometimes you make mistakes, so what, everyone does.