Question about UK Council Tax benefit when sharing a house?

It depends by what you mean by sharing the house, if you are what is termed a lodger you are not liable for council tax at all. If the landlord considers this his main residence, then he is liable. If however you are renting the house that is a different matter, the landlord becomes your lodger. You need to go to the council and explain exactly what is going on. If he is receiving rent for the house, he is not liable for council tax.