interaction of tax credits, HB and ESA with temporary absence of one partner

I have a conundrum.

My client has a partner and child who he has been living with until recently. She works and they have a joint claim for CTC and WTC. The tenancy is in his name and he claims HB - she is included on his claim as his partner.

He has now gone into residential rehab for approx 6 months so there is a temporary separation.

He has put in a claim for income-related ESA which is being paid to him as a single person as he is not in the same household as his partner. However, the WTC counts as income reducing his ESA. In fact as he is on irESA this should passport him to max WTC - this would then reduce his irESA to nil so that he is no longer passported to max WTC. The WTC will then reduce which will bring him into entitlement for irESA again passporting him to max WTC and so on. There seems to be no way to break the circle.

They could decide that the partner should change to a single claim for tax credits (although as a temporary separation they should continue to be a couple). Then she would get the tax credits and he would get full ir ESA.

But then what about the housing benefit? This is continuing at the moment as a temporary absence of less than 52 weeks while in residential care. It is still a claim as a couple. Can he claim HB as a couple if the tax credits are not? If he changes the HB claim to that of a single person temporariliy absent what is the status of the partner - non-dependant?

Any thoughts on the best way to progress this gratefully received!