My 18th mo. old&6year cousin both have ocd, dont eat, arnt growing,&certain textures bother them. whats wrong?

when my 6 yr old cousin was a baby he never ate any foods and was a tiny little boy. barely put on weight and was short but still had enough energy to last a whole day. he would try to put food in his mouth but the texture bothered him. my son also did this and hes 17 months old. when my cousin was younger he didnt like to get dirty or be around certain textures. like itchy material, ect. same with my son. my cousin would line everything up. including all his toys. very precise. same with my son. they were both and still are extremely whiny. im a single mom, so i thought i was spoiling him but idk hes extra whiny then most babies. he was colic when he was a newborn. never took to a pacifier. tried a lot of different formulas, bottles, and , and still was difficult to feed. never really did baby food and we saw a speech therapist to help him with eating and textures. the therapist thought he was making really good steps but once we stopped going he went down hill. my son only eats certain things and only eats a little bit all day. my son can get mad quick and throw horrible tantrums and hurts himself but wont care. same with my cousin. he threw and still throws fits all the time. ive tried every type of discipline but nothing seems to work. but at the same time, just like his cousin, he can be soooo loving and so sweet. he cuddles with me, loves me, kisses me, hugs me, and says "mom" every where even if i move away from him to just go to the bathroom. hes def. clingy to me. he talks a lot of gibberish still and just today said " i see a bug" but thats the only sentence he has said. he says words like, truck, train, car, ball and small words like that. he takes one nap only for a little bit and has so much energy to last him forever. hes ornery and wild!! i compared the two bc i dont know if this something going on is hereditary or not. but i def. feel like something is up. i dont feel like something is horrible but idk what to do anymore. if this sounds familiar and there is a name for this, let me know please. thanks.