This is going to be fairly long to avoid drop feeding so appolgies in advance.
Over the weekend I had my nephew over to play. He is 7, the same age as my eldest DC. He is an only child and whilst he can be absolutely lovely, he hates not having all the attention for himself at times and my DC's always have to do what he wants. Saturday appeared to be one of those days. He was very boisterous and was acting silly, swearing and being aggresive towards my two DC's to get their attention. My DC's were trying to play nicely on the trampoline (which they have just gotten) and were trying in vain to get him to join in, he very obviously wasn't in the mood for this.
After the 5th time of being called by my DC's, I explained to DN that his behaviour wasn't acceptable and he should apologise as we don't swear and hit in this house. I did not raise my voice and talked to him in a calm, measured tone. My mum was there and commented that she didn't know how I didn't lose my temper with him. However DN went mental and started shouting at me that I can't tell him what to do and that I'm a stupid cow with a stupid funny face (I have a slight facial paralysis). I was really shocked and upset and calmly told him this and that I was going inside to calm down as I was angry.
Everything calmed down and my DN left in what I thought was good spirits. Later that evening I received a phone call from my brother shouting and swearing at me saying how dare I discipline his son and that I humiliated him in front of everyone. His son is heartbroken and crying his eyes out because I was nasty and shouted and screamed at him! WTAF?! He then said that he was putting DN on the phone so I could apologise to him. At that I put the phone down. He has been ringing back and leaving nasty texts since then.
My mum has now got involved and has told me to apologise just to keep the peace as she hates conflict, even though she concedes that I didn't do anything wrong and handled things better than she would have. My brother and SIL are very bullying and domineering and this time I have decided to dig my heels in as I am sick of their behaviour which is obviously rubbing off on their son. My mum is now in the sulks with me. What should I do?