@Creamandjamorjamandcream Please, please, please, don't offer for your DH to stay back in the bedroom with the children. If your brother isn't that bothered about you being at the wedding, and he can't be or he wouldn't allow this horrible and very selfish rule - even if it was first thought of by the bride - then why would you attend his wedding at all?
Just because you will be staying at the same hotel as the wedding party, and where the wedding is actually taking place, it does not mean that you have to attend the actual wedding. If your Dear Parents are going to be there, and they are putting pressure on you to attend, please explain to them (again if necessary) why you won't be attending it, and tell them gently that it is your brother they need to have words with if they don't like the situation as it is at the moment. But please stay strong, and don't give in.
If your brother doesn't change his mind, please tell him that you will all still be staying at the hotel,and will be going "no contact" from now, and will stay like that until he profusely apologises for his and his future wife's behaviour over this - you might have to wait until their first child is born to receive your apology.
If after the wedding and the meal - I suppose I am being presumptive here - you want to meet up with members of your family, then go into the bar, have some hopefully free drinks, and a dance if you want to, and stay strong and ignore your brother and his wife if they approach you.
Why do I care? I care because I had a very similar sounding brother who lived overseas for most of his adult life, got married, had children, came back to the UK for 1 to two weeks, almost every year, but he would only spend one night a year visiting my parents - who loved him very much. As my DMum neared her death bed she asked me and my husband whether she had a son, that broke my heart, but I have never told my brother that, just incase it did upset him. He didn't even come home for our Dad's funeral. There were things done by him later, when my parent's house was being sold, that also broke my heart - it was nothing really to do with the actual inheritance, which we split equally as was written in the will.
I know that your brother isn't my brother, but I have hope for you OP that if your actions regarding the wedding work, you will be giving your brother the opportunity to think very hard about his behaviour, and what he actually wants the rest of his life and relationships to be like. I don't even know where abouts in the world my brother lives, or even if he is alive. He will be in his 70's if he is still alive.