Help with dementia please?

Can any body please help me , my mum is 86 and has been diagnosed with vascular dementia , i am her carer and have a young family of my own, my dad lives with my mum and is 84 and in poor health himself so i care for him as well . II gave up work last year to devote more time to them but i am at breaking point problem being that my dad wont let any outside help through the door , can any one advise of any help that can be offered as social services don't seem that help full and financially i am sinking as i only get carers allowance and my petrol bill is over �70 a week also dad is struggling big time as mum is becoming dangerous around the house , any advice or help would be great