I think this is done on a case by case basis. I know the DWP often come out and interview you and check the living situation. The HMRC might do the same.
It might be harder because you are married. It’s worth calling them up and explaining the situation or explaining the situation with another A4 sheet with the application form.
I know splitting things 50/50 sounds fair but it is only fair if you both make the same amount of money. It’s not fair when one of you make £40 a week and the other makes £60 a week.