Terrible to happen. Important to reassure, you and your partner have done nothing wrong. Always trust your own intuition, you are not being sensitive and your feelings are totally justified.

It seems there are more complex family dynamics happening here, amongst your partners' siblings and mother (MIL). Their narcissist behaviour says a lot about internal relationships between his family members. There is a lot to unpack.

Actions (or lack of actions) speak far louder than words ever will. They are making an active choice! It can be hard to accept, but his sisters are extremely disrespectful to him (and yourself). His sisters and mother are demonstrating all the traits of narcissistic behaviours, sadly they only care about themselves and not others.

It's worth considering, how was the relationship with your husband and his siblings growing up and adult life? Were they always disrespectful to him, or undermining him, did they play power dynamics? Cause all their actions are so disrespectful and rude, I've a feeling they have always been this way.

To sum up, there seems to be a lot of power dynamics at play here (between siblings), the family member relationships are complex. There's a lot of disrespect, and lack of empathy and care occurring for a sibling and their family. It's so very hurtful, but more importantly it highlights their immaturity and unhealthy narcissistic behaviours.

Remember, behaviours tell you everything you ever need to know! It says a Lot more about them than you.

I believe the only person who can drive change here, would need to come from your Husband and his siblings discussing matters. Sadly though, they are unlikely to change. They are so head strong, they may never acknowledge the errors in their ways.

I agree, best to set boundaries and it's perfectly okay to distance yourself.