Housing needs for 2 daughters with severe Autism

Hi all. First post here so here goes. I'm hoping someone can assist and maybe point us in the right direction.

Ok we are a family of 5. We have 3 daughters aged 8, 4 & 2. The two youngest have already been diagnosed with severe 'classic' autism. The 4 year old already attends a specialist autism school for 3 days a week (moving to full time this sept)We are in receipt of dla and my wife also receives carers allowance for both.

Housing wise we live in a small ish 3 bedroom new build which means our youngest has to share with our eldest. We can't put the 2 asd siblings together due to them having meltdowns when they are anywhere near each other. The problem we have is they desperately need their own bedrooms due to the sleeping issues the 2 youngest have. They are frequently waking our eldest and it's effecting her general performance at school. It's open plan downstairs so we have no way of separating them when they have meltdowns with each other.

So that's a bit of background. The question I have is as our house is unsuitable for adaptations I wondered what the possibility is of being moved into a bigger house by our local council? We currently own our house and we cannot afford to move to a bigger house due to us only being a single income family and simply can't stretch to a bigger mortgage.

If it's possible we qualify for a bigger house I still have no idea how to get the ball rolling about asking/applying. Do I ring the council? Fill out online forms, who to speak to etc etc. Our doc has said she will provide a supporting letter advising we should be in a bigger 4 bedroom house but as I mentioned I've no idea how to start all of this.

Any help much appreciated. For the record we come under South Ribble Borough Council.