You have a problem there perhaps you could mention he and your mum attend counselling together and put to rest the differences. Or mention to him every one has different opinions and we have to learn to live with them. Then there is the response. Hell mum wouldn't say something like that you might have miss understood. Or, you must be feeling quite down because normally you are a great guy, go talk to mum about it. Not a nice position to be in as any comment you make he may turn to make it sound as if you agree with him and then you will be off side with your mother. There is always trusty 12gage
I had problems with my inlaws, Roslyns brother to be precise. He made a very rude comment infront of my guests three years ago which caused me to become a tad angry. I have not seen him since. I escorted him off the property. But I do know how frustrating family fueds can be.