It isn't you who needs to feel guilty. You discussed this with him and whilst it is doesn't surprise me that he would go back on his agreement and be so selfish, you at the time had no reason to think he wouldn't be capable of sticking to something agreed when you went in to request it.
I know you mentioned before as well that your trust doesn't allow you to only work night shifts so what did he expect as it wouldn't work of course to a night shift Wednesday and then day shift Thursday, doh!
I am glad his Mum is able to help and please don't feel guilty for the children or his Mum. It is his choice to have said one thing and done another. I'm sure his Mum will make sure they are okay and honestly it really does seem like she sees through him at least a bit.