Help seriously heartbroken and embarrass

So last night we had a big bbq at our home for my partners birthday. All my family we're invited and so were his and close friends of his that he considers family. 
As always people don't always get along but you expect them to be able to be civil at other peoples events and homes etc. we had specifically invited a coupe that recently went through some cheating issues. Their names Rebekah and Adrian - he cheated with Koulla. Now we don't know Koulla at all, never spoken to her in my life, however my sister is best friends with her. My sister was at the bbq. She invited Koulla into our house (didn't ask me) I didn't even realise Koulla was there until the fight broke out.
Rebekah decided to stay with her man after the cheating and work it out and it was the first time she has seen Koulla since it had happened, Rebekah went to pour her drink on her, her partner Adrian stopped her and dragged her out of the yard. She was outside hysterical and drunk etc.
A few minutes later my sister and Koulla decided to leave, my sister said to me " if this cunt is outside I'm going to smash her" as she thought she was going to protect Koulla from being hurt. Anyway sure enough we heard screams outside, we all ran out and my sister and Rebekah were about to fight, we all tried breaking it up. I was absolutely embarrassed, this is the first time my partners family have been around my family and something like this happens. My sister is very violent and just wants to fight people. 
My mum then started swearing at me and my sisters telling us all to get fucked for not choosing our sisters side. Now my partner was fuming swearing angry that this occurred and went on, it was a huge fight in the street and all the visitors were out there in shock trying to stop it and also just watching. 
I have been getting abusive messages from my sister all night after it happened saying she is coming over tomorrow during the day and whatever we have to say about her we can do it to her face and she will flog me because I'm a fake cunt and all this crap. There's 4 other sisters as well and we all are so embarrassed and don't agree with what my sister did or the fact that my mum was thinking that it was accoeyable for my 30 year old sister to be doing what she did.
I'm soooo thankful my kids were not there, that's disgusting behaviour and not something I would want them to witness. Absolutely heartbroken that this all went on. Don't know what to do now but nervous my sister is going to come around today. Please any advice? Was I right in saying that my sister was in the wrong?? 
I felt like my sister shouldn't have brought Koulla there knowing that our guests Rebekah and Adrian were invited and we didn't even know Koulla ourselves. It was as if she knew something would happen and that's exactly what she wanted. At the end of the day it had nothing at all to do with my sister, if Rebekah wanted to fight Koulla then that is their thing but for my sister to get involved and fight Koulla battles??   And my mum to think it was appropriate and not try to stop her daughter?? Then our mum to turn on us because we didn't agree with what was happening.