I have 2 adult DDs at home, finished Uni, working and saving for housing, and I charge them £30 weekly. I won't take anymore as I want them to get a foot on the housing ladder, also they're young..let them go out, holiday etc as well as working and saving. You're young once and it goes quickly.
I have a longterm DP who doesn't live with us, but he's here a few times a week so he buys all the household food etc shopping.
Your post made me think of my neighbour, whose son left home suddenly. Not saying this is/could be your situation btw OP, just that it's a 'Rent' situation too.
Neighbour has a 7 year old, as well as the 20 year old who's left home (different dad). 7 year old's dad doesn't contribute - but he's round there a lot, they have on/off relationship.
Her son told my DD he was fed up of contributing as if he were the man of the house, whilst this guy is chilling with his mum..& mum asks son 'have you done dishes/taken out rubbish/done chores' etc when there's a grown man who should also be contributing. Should be 3 ways. So son has gone off to live with mates.
Anyway..if you need the money OP then no shame in charging rent as long as you're fair