Council Tax disregards
Some of these are if the only other member of the household is under 18, or you are a carer for the other person and they are not your partner, or if the only other adult in the household is counted as having a SMI
(Severe mental illness) this includes if they have Dementia or Parkinson’s Disease.
You can apply if they have a formal diagnosis and are receiving a benefit such as Attendance allowance.
The government site gives full details