Please help me!!! Family members (cousins) being really nasty about 7year old.

Hi, my nieces have been really vile to myself and my son. Calling him all the names. They don’t understand him, he’s not been diagnosed with asd as yet but does have a learning disability diagnosis as well as verbal dyspraxia. So last night, we had a family party, for which I was working behind the bar and didn’t know my nieces had arrived without their mum. my son and his friend were making some noise bouncing on a metal grate, my niece whose 19 and pregnant and had been in a car accident on Wednesday, (although my son didn’t know that as I didn’t want to scare him) asked them to stop which of course they didn’t. My niece then takes it upon herself to shove my son which results in him kicking her in the back. Josh is told to apologise, so he hugs her, she promptly says argh and pushes him away again. At this point it blows out of control. My three nieces start shouting at me whilst I’m working at the pub.  I’m then told I need to learn to control my (edited by moderator) child and teach him from right and wrong, he can’t go around kicking people and hurting them; He’s a c*** and a ***. The messages I’ve had are awful! These are just a few snippets of what’s been sent. I call their mum, my sister, who says it’s my fault and their step dad will come to see what’s going on. They never showed up. My husband, was sorting this situation out but at no point did anyone tell Josh what had happened to my eldest niece. I stated god forbid her unborn child has any additional needs. She then told her mum I had said I hope her child has additional needs! Now I would never say that as you don’t need me to say how bloody hard it having a sen child. So my question is are there any resources to help my family understand josh’s needs better? It’s been a really crappy week, new school for Josh meaning he has to get a sen taxi, he hates it and had been crying every night and morning begging me not send him, he’s mentally like a 4 year old. Just feel like the worst mum in the world and just want the best for him! I work within the educational system and know their will be tons of resources on unspoken language or something like that, from neurotypical people to people with sen needs but I can’t find any relevant. Although, I don’t think it will help as they just don’t understand josh.