A8 and UC - Complicated A8 query

Lithuanian couple came to UK in 2010. Mrs worked for just under 5 years.  Mr is disabled and receives DLA and Mrs gets Carers Allowance and Income Support and HB.  20 yo son and partner with a child. - he works part time.  They live together and the older father claims HB.

We haven’t seen all their paperwork and are wondering if the older couple are entitled to benefits on the basis of family member i.e son being a worker? What would happen if son and partner moved out? Would father still be eligible for HB?  Also will happen when they migrate on to UC?

Would it be better if son and partner were the tenants and HB/UC claimants?

You need to go back to Mrs and her work - came 2010, was any of her work pre May 2011, if so was it registered (if not this is not fatal) and go to what happened when she stopped work - did she retain worker status?, once got 5 years legally residing there is a permanent right of residence.  Mr, assuming married, will have his wife’s right to reside.  Advice is to get the whole work history and what happened during any gaps and from that do either husband/wife fit permanent residence.