I'm so sorry ..... and so sorry you have been dragged into this. I feel angry with your sister for placing you in the unenviable position of holding such knowledge - and having to deal with the emotions it arouses.
You have to wonder on what basis this abortion was granted. I presume on the assumption that the mental health of your sister would be affected were she to have had the child, as it wasn't on physical, medical grounds relating to either her or the baby. It's cases like these though which make me question the whole abortion debate (I appreciate it's often not as simple as balck & white) though because it seems too easy sometimes - and on the balance of probability, I'd hazard a guess that if your sister's mental health was going to be affected, it's more likely to be as a result of having the abortion, as opposed to keeping the child ....
.... in truth, had she kept the child, her lifestyle may have changed for the "worse" (though would hardly have catapulted her into poverty by the sounds of it) and the "grief" from her bastard of a so-called fiancee may have continued. They may have split up. Do those circumstances really justify an abortion ?
The fact she's now "calm" because he's stopped giving her a hard time and she's relying on this 2 year plan gets to the truth of the matter. I can't help wondering what the clinic would have said if she'd applied for an abortion on the basis that she wanted the "grief" from her fiancee to stop ? Kinda makes a mockery of the whole abortion rationale ...... to my mind, it should not be used as a form of contraception, which it clearly has been in this case.
I feel sorry for your sister but I also feel very angry with her, when she was in a far far better position than many women who unexpectedly find themselves pregnant. If, and it's a very big if (because I don't believe it will happen) the pair of them ever go on to have a child, then what on earth will the point of this have been ?? You have an abortion (amongst many reasons) because you're with the wrong person (well, she is, but she doesn't think so ..) or because it's the "wrong" time (as in, say, you are living on an extremely low income and a baby would push you over the edge, but that doesn't appear to apply), or, because you don't want children at all (she does, he doesn't - so should get the snip (or castrated)).
The ONLY reason this has happened is because he is a selfish, bullying, emotionally blackmailing bastard who thinks only of himself and is prepared to use his existing children (and what will they be told about this ? Will your sister have had a "miscarriage" ? Will they be told the "truth", but your sister will get "blamed" for it ? ..... I can't see them being told that the baby was destroyed .... no, ..... killed because their dad was more interested in fancy cars ) to get what he wants. WHY would you have a child with someone like that ?
I guess I feel angry that your sister and this pathetic, nasty excuse for a man have actually abused the "system". Abortion laws weren't designed to assist adults capable of being responsible (in theory) for their own fertility, who were stupid enough to get pregnant and then declare it a mistake - him, because he's a selfish git who should have put his money where his mouth was and got seen to (though I have this nagging gut instinct that this twat might be the sort who sees vasectomy as some sort of threat to his manhood, and is therefore prepared to take risks and worry about the consequences later) - and her, because if she wants a child, and is capable of supporting one (albeit without the nuclear family, roses round teh door fantasy) then to have gone ahead on the say so of someone else (as opposed to it being her own free choice) seems very hypocritical and very cruel.
I shall be astonished if they haven't broken up within months. She might be putting on a brave face at the moment, sweeping this under the carpet and pinning all her hopes on a 2 year plan (she should actually be questionning why a 2 year plan is apparently necessary ??) but I can't believe that she won't be hugely and adversely affected by what she's done. She will start to hate him, if she doesn't already and I can only assume that she must have incredibly low self esteem if she's prepared to let this bastard dictate something of this enormity to her. As for him, he'll have been squirming these past few months and will feel like celebrating now, I bet he thinks he's had a "lucky escape" (thanks to his convincing lie about 2 year plans to twist her arm) but if he's not thinking it already, he'll soon come to regard her as a huge risk to his hedonistic lifestyle (she's got pregnant once, she can do so again) and if he's not honest enough to break up directly, he'll be nitpicking away at everything she does until she makes the decision to go instead.
This is one of the most upsetting threads I've read on here and again, I'm so sorry you've been dragged into it. She may have felt confused, and had a need to talk, but there are impartial, trained and professional 3rd parties she could have turned to instead, so you would not have had to deal with all this angst. I wouldn't be telling tales so to speak on her to the rest of the family, but on the other hand, were any of them to question your apparent coolness towards her and this "man" (I refuse to call him an actual man) I'd have no qualms then in explaining why.