It sounds like to me that he might be angry at the two of you for some reason.
Not saying that it’s for good reasons, because many people can be quite irrational.
I have a brother in law like LoD's oldest. He was raised by wonderful, giving, loving, Christian parents. If you talk to him and my wonderful husband, you would think they were raised in different families! My bil accuses his parents of being abusive and hateful, and nothing could be further from the truth. He hated them passionately, and left the family at age 17, only briefly touching back when he needed some form of help.
Now, you could give him the benefit of the doubt, and perhaps assume the folks learned how to be better parents or whatever, but you really have to look at the whole family dynamic. I knew the parents well, and know how they grieved their oldest's feelings. I also know how well my honey turned out. The real key though is that my bil is so toxic a personality that we have had to sever all contact with him. I believe something in his childhood caused him to get angry at his family, and he was never able to "grow up" or get over it. It is almost as if his emotions are those of a spoiled 7 or 8 year old, and his temper tantrums are those of an adult.
Liberty, I hope you don't feel guilty. I believe my bil needs medication (or deliverance), and I don't feel guilty about cutting him from the family at all. I know my husband misses his big brother, but he also recognizes that he is dangerous to our family, on many levels. That, plus you can only take so much abuse before you declare "enough".