SDP and joint tenancy

Probably clutching at straws here. 2 brothers secured council tenancy on their mother’s death (i.e. took over her tenancy of family home). Both joint tenants from day 1 of liability. Nobody else living there. Brother A is awarded DLA mrc 10 years later. Brother B is not a non-dependant (and so SDP payable) if the following condition is met (other exceptions don’t apply):

‘Where a person is a close relative of the claimant…paragraph 2B shall apply to him only if the claimant’s…joint liability to make payments to a landlord in respect of his occupation of the dwelling arose…on or before the date upon which the claimant…first occupied the dwelling in question.’

They were already occupying the dwelling before they assumed liability, as non-dependants. It would seem that normal residence (whether liable or a non-dependant) would define occupation. The straw I’m (probably vainly) clutching at is whether occupation could be defined as when they first became liable to pay to occupy.