Where can we get help? Late ASD diagnose and the family desperately need help

I have a 25 year old sibling who was diagnosed a few years ago as having ASD. They are deaf and still live at home with my mum. They have some serious mental health issues including confusion around their gender which we are desperately trying to get help for. They have refused to see any medical professionals for so long and finally agreed to get some counselling or similar. However, due to the pandemic the service would only do video calls which weren't accessible for my sibling. They finally got a face to face appointment with mental health services this week but when they went along, the professional didn't turn up because they assumed it was a video call. Every time one of these set backs happen it is so difficult to persuade them to continue with seeking help. 

They have self harmed and have suicidal thoughts. They are violent, rude and so so horrible. The insults and things they say to my Mum are horrendous. She feels bullied in her own home but cannot do anything because there is nowhere else to go and no help available. My sibling is intelligent and funny and great company when they are in the right mood but the entire family has to walk on eggshells as not to trigger them. They will explode over the smallest thing, destroy things, punch and kick holes in the wall, push my mum (they are physically a lot bigger than her), make threats, cry, scream, shout etc. We've been dealing with it for so long and I am so worried we are at breaking point. 

I am so worried about both my sibling and my mum. I worry for her mental health as she is so isolated and trapped in this situation where she is being bullied and unhappy all the time, but of course she loves my sibling unconditionally and wants to be there for them. I worry for my sibling who is so confused and unhappy about a number of things. I desperately want both of them to be happy and to help them get any support we can. My mum will not go anywhere because she is terrified she will come home and find my sibling dead. This is having a huge effect on her mental health and mine as we are living in a state of constant fear.

We have no money to look for private help. They live in a council house. We are reliant on the local health services which seem to be so slow and I am worried it will be too late before anything gets done. What can we do? How can she get some respite? Is there any charities that will help? Is there such a thing as assisted living for those who are high functioning but have mental health issues and aren't independent.

My sibling doesn't go out and socialise. They are constantly anxious. When my mum leaves the house she is bombarded with text messages often abusive. She gets carers allowance for looking after them but still needs to go out and work the hours she can because the money isn't enough for them to live on. She is run ragged tending to their demands and I just don't know how to help her and my sibling to get into a better place. Please let us know if there is any help available as none of us can cope and continue like this.