It won't help solve anything to break this difficult situation down in terms of right and wrong, bad guys and good guys, even though that's what seems to be happening on the "other" side of the family. You're certainly not wrong in not wanting to be the scapegoat for the family's discontent. That takes more grace and patience than most living, breathing humans are able to muster.
I'll give you the same suggestion I just gave another mom – a process called Non-Violent Communication that can do wonders (with some time and attention) in difficult family situations. That is assuming you actually want to try to maintain a relationship with your in-laws. It sounds as though your husband is even ambivalent about staying in touch with his family. Pulling away until such time as you feel willing to face it again is another possibility, although you could invite even more blame and anger. But you can probably distance yourself from it. You could even make it clear that you are doing this until such time as the family can talk to you with respect and compassion, as you would like to do with them.
I'll bet your in-laws perceive that some legitimate need of theirs is going unmet by current family dynamics, and perhaps are not clear enough about it to say what it is, or what can reasonably been done about it. This is a common human condition, which unfortunately often results in mind-reading and projecting confused or ugly motives onto others. Since you're not there participating in the conversation, you don't have the opportunity to moderate their misapprehensions.
I hope you'll check out a practical and effective communication technique called Non-Violent Communication. You can learn a simple, 4-step process that teaches you how to talk to anyone compassionately and respectfully, so that you don't add to existing negativity. You can help everyone concerned become more clear their own needs, and help tease actual feelings and needs apart from all the ideas we have that get expressed as "should" and "oughts.". You can learn how to make clear and unbiased observations that will support, rather than undermine, further communication. And you can state your feelings and needs in a way that allows the other person to hear them without feeling attacked or overwhelmed, and becoming defensive.
While it does take a bit of learning and practice, Non-Violent Communication is worth the effort, and can be effective even when used by only one person in a relationship. If this interests you, you can google the term for books, classes, summaries and examples. My husband and I have both learned these techniques and find them transformative in understanding and communicating with others, and even in understanding ourselves better. Good stuff! My best to you all