AIO for communicating with sister in law about her husbands behavior toward my partner?

Probably going to be a long post, but here’s some context. Me and my partner have been together for 3 years and have a daughter. My partner owns part of a business with his sister’s husband. They have one group chat for owners, and one for the employees which I am in the latter.

Lately, her husband has been undermining my partner in the worker chat which is pretty unprofessional imo, and rubbed me the wrong way. The workers are constantly disrespecting my partner and they seem to be following suit from his brother in law. He’s addressed it in the past, but his brother in law has a big ego and does not take any criticism well, so it has blown up in the past a few times.

I reached out to sister in law per her request, since in the past her husband has thrown fits anytime something he’s done is brought to his attention so she asked for us to bring it to her instead since she’s better at communicating with him. Sure, no big deal. I asked her if his comment was necessary, and that it’s been a pattern I’d been noticing for a while now and if in the future he could either mention it in their personal chat or just not say anything at all.

She proceeded to make excuses for why they have been frustrated and stressed. I explained that okay, they are stressed, but that does not take away from the fact that the disrespectful comment could have been sent separate from where employees could see it, or he could have reworded it to where he didn’t sound like he was being rude and ugly.

She went straight to their entire side of the family and blew it out of proportion. Accused me of trying to cause fights between her and her husband, and then started a new work group chat with the employees that did not include me.

AIO for trying to stand up for my partner, when this has been going on for so long and I’m just so tired of her excusing her husband’s behavior toward her brother?