House keeping

Of course they should be paying. They've been there a year? Put their rent up and give them six months to leave. Even if they aren't working (and why not, unless they are students?) they should be contributing. You do them no favours letting this slide.
A discussion about their future plans is needed here.

Regardless of their income they should be paying something to food and bills without question. How come there’s no room at their parent’s house, did they not grow up there?

This should have been dealt with after the first missed payment. They either pay up or find elsewhere to live. Both are of an age to be working and contributing - not to be getting a free ride from grandparents. Smacks of entitlement.

Not unreasonable at all if they are working but as I’ve no idea if they are working or not it would need more info if they are not working it would depend what aid they are getting as to the amount

Are you being unreasonable? Absolutely not!

If you are paying all the bills then they should be contributing - why did they stop paying?