@Ali Alsaadi
Hi, I’m sorry you’re going through this.
As for your mom there’s absolutely nothing wrong with looking at her and admiring her and her beauty, she’s your mom. I always look at my mom and I’m like I love her she’s so cute but never in an incestuous way, cause that’s my mom and that’s gross. As for your sister it’s literally just like your mom but maybe more like sibling love. Like you can look at your sister but again not for incest reasons, be her brother; play games with her, do HW together, watch tv, don’t ruin your relation with your sister. Again, that’s your sister and it’s weird to have these thoughts about family members and it’s not haram to look at them either.
As for the girls at school, I mean you guys are 15 how bad could they be dressing? Anyways just try not to imagine every girl you see as a potential candidate for ‘you know what.’ Think of them as actual humans rather then just a piece of meat. If you look at them without lustful thoughts then it’s okay to look at them. It’s not haram to look at people.
I know that’s easier said than done especially with your OCD but just know that you’re not a Kafir and God would never put you through something so difficult. Islam is supposed to be easy but sometimes us humans love to complicate it. Walk with your head held up high boy!