Not liking step son

I feel bad and childish for feeling this way but my SO son annoys me so much when we have him. He’s 5 and acts like a big baby. Some days he annoys the hell out of me and other days I’m being super sweet and loving to him...If I didn’t have my new baby I think things would be fine but just everything he does annoys me. He wants to hold her and be in her face and touch her. I let him hold her some times but I always get him to wash his hands because he puts his fingers in his mouth, nose, digs up his butt. Kids in general are just not the cleanest and full of germs and especially with these new viruses going around. I want to protect my new baby at all costs idc who they are. I also don’t like it when he’s right there when we change her diaper. It makes me uncomfortable cause idk if his parents talked to him about boy/girl parts and he’ll be staring when we take off her diaper so I make him get away when we’re changing her cause I don’t want him staring at her vagina. My SO thinks I’m being extra and said he’s just helping which is fine but he doesn’t need to be in her private area. He doesn’t even watch his son wash his hands he just tries letting him holding my baby and I always stop it. He swears his son can wash his hands so one day I watched and all he did was squirt the soap in his hands and then rinse it right off. No lathering or anything so I had to teach him the proper way. And then his son doesn’t act or talk like a 5 yr old. He’s babied so much he talks like “my tired, my hungry, me don’t like that” or “hers spit up, hers stink” and when I corrected him and asked why he replaces “I” with “my” his father was like “tell her we’re still learning “ what??! How is it learning if you’re just letting him talk like that and not correcting him??? He’s going to start school soon and that’s how he talks??? Smh I tried doing flash cards with him and would ask him to read a word. He thought every word said dinosaur...even the 2 letter words. Smh and he’s so loud I have to constantly remind him baby is in the house so stop yelling or running and he’ll even run into her nursery when I rocking her to sleep when his father is chasing him playing. I feel bad for this but I wish he didn’t have a son.