Be assured of one thing: when an adult child returns home to live with the parents, it will not be an easy transition for anyone. There should be rules agreed upon by all parties beforehand, and they must be conscientiously followed, until such a time as everyone agrees to change them.
It is a good idea to have the rules printed out, laminated and posted in a prominent location in the home. It is not that the parties involved cannot be trusted, but the rules, hanging in plain sight, will serve as a timely reminder.
The returning child is probably, in reality, an adult and must be treated as one. I will speak of him as male, but it could just as easily be a female.
The rules below are only suggestions and can be adapted to each family's circumstances. Speaking from personal experience, they have worked well for this writer.
Each party must have as much space to themselves as possible. A downstairs apartment for the returning child is an ideal arrangement, but at least a bedroom should be designated as his, and his privacy should be respected. Visitors must knock before entering. He should not be hassled to clean up his room unless there is an actual fire hazard involved, or an unpleasant odor begins to waft through the house from his area.
Certain rooms might be shared: the laundry room, the bathroom, the living room and perhaps the kitchen. The child may eat with the parents or be responsible for his own meals according to how schedules can be integrated.
If he is expected for a meal and can't make it, he should notify his mother as soon as possible.
He should be responsible for his own laundry.
Probably a shortage of money was one of the reasons the child returned home. If he cannot pay board or contribute to household expenses for the time being, he should offer to help out with housework and yard chores until his financial situation improves.
He must be actively looking for employment, no matter how far below his dignity he considers possible jobs to be. Washing dishes or flipping burgers will be fine while he is looking for another position. He will at least have spending money, and there is always the possibility of a promotion.
Parents have the right to impose certain rules for their home, such as no overnight visitors of the opposite sex, no smoking anywhere in the house and they may insist that quiet will reign after 11:00 P.M. every night.
The adult child need not account for comings and goings to his parents. He should have his own key and be free to come in as late as he wants, as long as he is quiet.
An adult child returning home to live should be treated as an honored boarder. He should have his own space and be responsible for his own maintenance. He may share meals with the family, but should contribute to groceries and pay at least minimal board as soon as he is able.
The parents must treat him as an adult. They must refrain from giving orders as if he were still a teenager and allot him his own space and privacy. If he oversteps the agreed-upon boundaries, they need only go and point to the house rules which they laminated and hung on the wall.
It won't be an easy arrangement, but it can be done if all the parties involved treat each other with goodwill and love. When the young person gets back on his feet and moves out, they may all look back on these days as the period when their relationship moved from that of parents and child to that of trusted adult friends.