I just found the 'strap line' Have a look and see how much you could charge your adult children.. the whole concept of parents wanting to see how much they could get away with is unbelievably distasteful.
Surely parents want to help their children as much as possible. Some parents are lucky, have high incomes and no mortgage.. or low outgoings and can afford to host the children for free. That's great if you are in the position to do that .
However there is absolutely nothing wrong with charging AC a reasonable rent - but surely reasonable ends at the point where you 'profit ' from them being there. So if you are already paying rent /own house for a property with spare bedrooms and had no intention of moving - then reasonable is an equitable share of utilities and council tax.
If the intention was to get a smaller place to save your rental expense - then the difference between the existing place plus the utilities- is fair.
The moment you profit from your children- your moral compass is screwed.