Recovery of housing benefit

Other

We had a tenant who recently died in hospital unexpectedly. While he was in hospital his housing benefit, which paid his rent, accrued in his bank. He was unable to pass the rent to me as could not carry out his banking from hospital, but assured me he would sort this when he returned home. Since his passing, family who have never visited in 20 years, are now in control of his bank account. We have informed them that there is an amount of money owing on the flat within his bank balance which was housing benefit. They have now told us they are not prepared to pass the money on and intend to keep it.
Should the local council who issued the housing benefit request these funds are repaid then we may subsequently claim it?
By what other means can we claim this from the family member?