[happy_doughnut]

I don't know if there's anything that I can say that would be put in better words than the ones already said.
Vicious, Fortune, and Azuma all gave you some very good advice, and not to mention encouraging words.

I know it can be difficult to *open up* to people at times. Hell, sometimes it proves to be nearly impossible. However, you should know that no matter what, there's always someone out there willing to help you, even if that help means listening only.
Keeping things like this, because this is a very nerve wrecking situation, inside of you will only lead to an eventual burst of anger, which you seem to be on the verge of fulfilling.

Like Fortune said, I know the words "try to not think about it" may sound to difficult to do, but it really is a good solution, especially considering the types of persons your cousins are.
Calling you names only shows their immaturity and stupidity.
If you show them how molest you are, it'll only make them feel the more grand. However, you musn't be too passive, or else you can wind up in another bad situation. Lay down the grounds for them; let them know that they're irritating you and that you aren't willing to take it. It's very likely that their responce will be a mockery of some sort, but at least you will have done your part.

It's a shame your mom has to endure problems that aren't even legitimately her own. It seems to me that the only one who desserves to put up with such nonsense is their father; not your mother. If for some reason she is willing to care for them, don't let her do it for free ! Make them haul their own weight around there. It's not fair that your mother has to work twice as hard for some teenagers whom are too lethargic to work for themselves. If they're going to be taking up space; make them pay for it.

Also, I'd like to suggest you speak with your mom directly. I know sometimes things are just much more difficult to express in words, but sometimes it's simply the best way. Try to console your mom and let her know how you feel, because only then will you reach a satisfying agreement.

I hope things turn out well for you, Chara. Just remember to not give up and to never lose hope