I myself am the youngest in my family, and I have to share a room with my older sister. I always come off as annoying. I never understand why, I often ask questions about things because I just want to know. I'm not trying to irritating by not understanding. '-' I come off as annoying, because maybe i ask too much, or a joke around too much, people say i dont know when to stop etc etc.
I've never been annoyed by anyone. But everyone tells me I'm annoying c: Perhaps you could try seeing it from your siblings point of view sometime?
Another thing.. are they really doing it on purpose? Poking, asking stupid things, coming into your room, etc etc. Is she trying to be annoying? Or is she bored, is there nothing for her to play with (Idk her age), no one to hang out with? Maybe she just wants attention?