I would make very sure you talk to your parents about him opening your bedroom door without asking your permission first, ditto the bathroom door. That can lead to some pretty serious problems.
Is he really in charge of you kids, like a baby sitter?
Did your parents give him that job? Or is he over-stepping his limits of what they have defined for him to do? Your parents should make that VERY CLEAR. They need to sit down with both you and him TOGETHER, speak clearly, and be very, very clear about what his responsibilities are in this situation and what yours are.
In some of the situations, I think you could have been more polite and respectful, even though you don't like him. He is an adult and you do need to respect him. Yes, you even need to be 'decent' to people who are somewhat clueless according to you. You don't have to adore someone to speak politely and in a calm voice to them.
You should not judge him because he has trouble keeping a job or hasn't been there for very long, that is not fair - he can't help that. Forget about what else he has or hasn't done in the past, and make sure you only address the here and now. So he did not know the sister didn't know a word - that is not his fault. Most adults would assume a child had been taught that word.
You should however, tell your parents if he EVER comes in your room (or bathroom when you're in it, or any of the kids, for that matter) without knocking, without making sure you are fully dressed, and that means knocking and asking to come in and making SURE you are dressed and ready to talk to him, and not coming in if you say you are not ready to see him. Don't abuse this right, don't pretend you're indisposed just to avoid talking to him, but that is your right with all adults.
That is ONLY allowed in an emergency - poisoning, choking, someone passes out, a fire or explosion in the house or other very serious matter. It is only ok to do so to deal with the emergency.
I think the problem is that to you he is a guest - an unwelcome one. But it is not really clear if your parents really appointed him baby sitter or not. If they did you have to listen to him.
A lot of times, the situation is not clear. A house guest arrives, and the kids don't like him. The parents might say could you watch the kids for a half hour or so - and it's not clear to the kids what the rules really are.
A lot of times, a house guest can feel like they SHOULD watch the kids, when maybe that isn't what the parents really expect. I don't know about anyone else, but if someone made me their house guest I would try really hard to make myself useful. I would try to watch the kids and I would try to entertain them, do dishes, cleaning, and watching out to make sure the kids didn't get hurt. And of course I would make some mistakes because I don't know the house routine. That's expected.