Me. Myself & i

So sick of being the mediator at home, why do i have to know everything when they don't like to tell each other? Maybe i shldn't be such a busybody at home, just keep to myself, don't ask them about their lives, rush off for work as fast as i can, come home real tired...
I'm not blaming them for doing what they are suppose to do.. but why has they become so absorbed by their own lives, that when they think they're being considerate, they're actually causing much more misunderstanding? They are all very generous, friendly and nice people individually. Why do they have to impose their idea of being considerate on others, such that it becomes more of a burden to each other?
She tries to bring her dad to doctor's appointment all the time because she doesn't want the rest of them to take off from their work. Being a tuition teacher, she doesn't want to burden the rest, hence she changes her schedule as and when to suit the appointments. Also, she is like the mother in the household, she cooks and clean and does all the household chores. Although she doesn't ask for anything back from her siblings, her efforts are almost always seen as "she took it up herself, she will redo it if we help anyway". A person who like to do things her way, her siblings know better than to help which she continues to pack herself with more work. The only problem is that, there is only so much that a person can do, and with all that stress she packed herself with, how does one expect her to smile all the time? Not to mention that she is a serious person by nature.
He has got a 9 to 5 job, as the eldest son in the family, he tries his best to be aware of what is going on. He tried catering to everyone's needs. He is stressed out himself, he is tired of accomodating everyone else. With most of his sisters married, he has to be the balancing force between his sick dad, his tempremental elder sister and his quiet younger brother. To add to this, he has a dreamy girlfriend who believe in living her life to the max while she is young. His sister cannot appreciate his gf as well as him, he doesn't feel the need to address that. As the 'mother' of the household, she cannot understand how can a lady, whom come to her bf house to play computer games and playstation, who always asks his bf to go restaurants and genting be ready to settle down, when she herself doesn't earn much.
His girlfriend thinks that his sister has something against her always, he thinks that one day things will sort themselves out. That everytime, when his sister has a 'black' face, it is because of her.
I say this is a perfect recipe for disaster.

To him:

You've told me before that once u put her into the position, she'll be forced to grow up. So when is she being put into the position? when you guys get married? or is it good enough now that things are more or less settled? I'm not trying to be nosy here, i noe very well that this is non of my business. But i don't want to sit here and watch the disaster unfold itself if i can help it. If today it is some other family showing this, i'll watch it like a drama series. I cannot let this happen to you guys. So just try to hear me out here.
I know it is difficult to come home and face her, you've also told me before. When met with difficulties, the easiest way is to run away from it. There is no way you can run from it, unless you want the problems between ur sister and you to pile up. I guess being the younger one, we have to always take the first step to make the communication. If you think that "she has made herself clear, she is so stubborn she wont change", den i can safely tell u that you are only waiting for disaster to happen.
Her "anal-ness" stems from the fact that she loves u too much and has been taking such good care of you that she don't know if your gf can do the same. She has an image of you in her head, one who shld be taken good care off, that you like to laze around the house, etc. She cannot imagine u, after u come back from work at about 8 plus, to be doing the housework. It is pressurizing to be loved like that, but can u blame her?
The pressure is there because there isn't any communication, there isn't any understanding. Since you have chosen yr gf, and she has chosen you, shldn't you guys try to get your sister's understanding? After all, she is the one who has taken care of you for so long, whether you asked her to do so or not. Frankly, if i can help you tell her that how you guys can work out, i'll be glad to help. But there is only so much i can do. I know it is frustrating to handle both of them, now it is already so evident, what do you think will happen in the future? You also told me before, you make the decisions, you face the consequences. This is one consequence that you have to face. Either you work hard at salvaging the relationship between them, or you lose this sister of yours eventually.

Stayin out wont save you. Your hopes that things will take of themselves will never happen. If all of you cannot let down ur walls, the pretence that things are always fine and beautiful, that you guys are independant individuals - i guess there isn't much me as an outsider can do, not to mention i'm merely a niece...