Yep... it needed to be said.. and he's mad because someone pointed out his failings. Boo Double Hoo. He's had a relatively easy ride so far, because you've very successfully kept the children at the front of your priorities in your dealings with him and are trying your best (despite his rotten behaviour) to co-parent amicably, because that is best for the children.
But now he's realising that not many other people are all that sympathetic with his bid for freedom and Tattoos. I bet your mum has been holding her tongue for a long time and I actually think because she's held back until now, he probably thought she was team Twatoo and he really doesn't like being held to account and made to face the facts does he?
So whilst I think you are right to ask her not to do it again.. I couldn't help thinking 3 cheers for Mum! Also. the tirade .... is him digging a hole for himself.. and I'd be so tempted to reply .."as I said to you in my text on Friday.. if you are annoyed with DM contacting you, take it up with her" and then keep repeating "As I said to you on Friday, and Saturday, and Sunday etc.. "
Re books. I love Audible as you can listen whilst you walk or do other things. and I love the Rivers of London series by Ben Abramovitch. Or The Vinyl Detective series by Andrew Cartmel. Or any good detective yarn really. If you don't have Audible. BBC Sounds have some excellent ones particularly loving the contemporary Sherlock & Co podcast, which has a new adventure every month. It's really well produced. But there's loads of good stuff in the drama section. Hope youhave a great weekend