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It sounds like things are going from bad to worse. Is there any way you could get some time away...maybe stay with your mother for a day or two? Sometimes a little time apart gives both people time to breathe and gain perspective.
The last time you wrote, the two of you had started being nicer to each other. Did something happen to change things?
It is starting to sound like Anthony might be having his own issues with depression. Being irritable, sleeping too much, lack of interest in sex...these are sometimes symptoms of depression. It sounds like he may be deflecting some of his own problems onto you, which isn't good for the relationship.
In terms of the in-law stuff, could the two of you invite that brother and his wife for dinner, perhaps? It sounds like things need to be mended there, on both sides. If that's not an option, perhaps both you and Anthony could chose one thing to do together for his parents. That might soothe the other brother's feelings, and show the family that you're both doing your part.