I am sure Ira can take it as good as he dishes it out
Money wise I think this is something that you should sort out now, as you say, they are under no obligation to pay the $25, and as soon as they are out the door, I think that you can kiss the good intent and money goodbye. Who in their right mind would pay $25 per week for nothing?
The new flatmates should be paying the same as the old ones, if not more, but never less!
Just remember, you have to fork out to fix the washing machine and find a fridge as well.