There remains uncertainty over what exactly GMP is investigating
I'm glad I am not the only one confused by this!
FWIW, this is my take on what is most likely to have happened. A young single mother, with a difficult upbringing, buys her council house. A couple of years later she gets married and moves in with her husband. But she still wants to leave her options open for a period. For some reason, rightly or wrongly, she believes she needs to reside at her own house to avoid paying back the RTB discount. So she takes steps to make it look like she is still living there, such as remaining on the electoral roll and paying the utility bills. As a kindly person, she lets her brother, who has struggled after serving in Iraq, live in that house for free.