I left an emotionally and mentally abusive man a year ago. My kids and I went to a refuge briefly but returned to our home once he was gone
He has scheduled times to have the kids. He's always been up and down about sticking to it. I have already spoken to someone about steps to take now including mediation
Lately he's let them down a lot. He was supposed to have them sleep over on Friday but was prepping his excuse and saying he'd let me know on the day. This time it tipped me over and I said no they won't be left dangling and took it as a no. We went away overnight last night and came back at lunchtime, partly since it's Father's Day. He messaged a few days ago demanding to have them this morning then blocked me before I could reply. He unblocked me this morning.
I spoke to him offering him time with the kids this afternoon but he said he and his girlfriend weren't available 
he was furious as usual
At around 11 his brother sent me a text insulting me as a mother and threatening my boyfriend (I feel too old to say that but also want to add the children have known him as a family friend for a long time and are fine with him). The threat was 'you wait til I see bob'
He's not implying a chat, I know him.
I've tried to keep this short and to the point, I am trying to arrange to see a solicitor from tomorrow. What If anything should I do regarding his brother?