Sick of being verbal punchbag

[cantdorightfordoingwrong]

I live about 9 hours drive away from my family (my sister, mum, etc) with my dh and dc (another on the way).
My sister and I are very different people (in every sense of the word, from looks right down to personality.). She's getting married next month and from the very start she's been a nightmare, I lost count at the beginning of how many times I got shitty messages from her because I couldn't just drop things when I was at work to find something she wanted online or because I would point out a dress wouldn't suit me (at my wedding she had full control of what dress she wanted but she was determined to put me in some kind of hideous blancmange type creation). I reached the point of just agreeing most of the time to prevent one of her inevitable hissy fits. However, before she'd even finalised dates, venue etc, I found out I was pregnant and due the same week as the wedding (didn't think it was possible for me to have another child so whilst very much wanted was very unexpected). I've had all kinds of guilt trips because neither me, DH or DC will now be able to go to the wedding - she could have moved it if she'd been that bothered but didn't want to (which is absolutely her decision).
As time has gone on, I seem to have become her verbal punchbag - I'll get streams of vindictive messages about how terrible I am because I've not answered my phone (I was out at the time) or because One minute she's ranted at me because she's had yet another argument with her DF and he's thrown something at her (they both have wicked tempers) the next I'm terrible for having said he was out of order. Then she'll do twisted little things like tagging me in pictures of baby items that she knows I will hate and saying "what about this?" Knowing full well she's persuaded my mum to buy it so when I go "no that's really not my taste at all" she can respond with "that's really not nice after mum has bought it for you!!!" And cause an argument there.
I'm due in a couple of weeks and been really struggling the past few weeks but yet again she started a row last night. She messaged me with wedding problems so I (in conjunction with dh) tried to give some constructive advice. The result? Another stream of vitriol about how she's telling me nothing else because I never have anything good to say and just have to put a downer on everything (just not phrased in quite so polite a manner, was full of personal comments and insults). I ended up in floods of tears cos I've just had enough of it, I know now inevitably I'll have days of my mum not speaking to me either (it's always been the way with my mum and her. Not to mention my mum is pissed off because I'm not going to the wedding - she expects me to travel regardless of whether baby has arrived or is a matter of days old. She's made no mention of even considering coming to visit baby here and has in fact kitted her house out with Moses basket etc implying she expects the baby to be taken there. I've got another child at school etc to consider, I can't just drop everything to travel 9 hours (that's without stopping with a newborn). I'm expected to do this yet sister hasn't visited us since 2013 and mum hasn't visited in nearly 4 years.
Sorry for the long rant, I guess I'm just looking to vent and/or get some opinions on whether I'm being unreasonable?
Thanks for reading

Block her
Life's too short to put up with this shit

What @Shoxfordian said

I honestly would just cut her out - you're getting nothing, literally nothing, from trying to maintain a relationship with her. I doubt she'd ever change so for your own sanity, focus on your DH and DC and leave her to it. You only get one life - it really is pointless to let it be ruined by her awful behaviour.

Absolutely block her OP.

How wonderful that you are having a child that you thought couldn't happen.

Your sister is ruining this wonderful time for you.

Block her and your mother.
The stress is not good for you or the baby.

Cut them off and mind yourself.
They sound utterly ghastly.

Best of luck 💐

This gets said a lot on here but I would grey rock her. It seems like whatever you say is wrong so if you still want a relationship, and don't want to block, you have to stop giving your personal opinion on things.

Eg if she says her fiancee did something, don't give advice, don't say he sounds awful, don't suggest she over reacted, don't say the obvious why the fuck are you marrying him when you can't go a week without a massive fall out, just say 'oh no that sounds really tough'. Don't give your opinion on anything your mum has bought. Try to disengage from all the drama. If they suggest you're travelling for the wedding don't explain or apologise just 'I can't/ that's not happening'. Don't be drawn in to any arguments.

And if that doesnt work then I do think you need to take a step back, it doesnt sound like you get much from this relationship

You need radiators in your life, not drains.

You would not have tolerated this from a friend and your sister here is no different. I would block all means of she and in turn your mother being able to contact you.

I would also think your parents have played a huge role in this development of this dysfunctional relationship in the first place too, your mother also sounds to be of no use nor ornament and she has not visited you in four years.