I would suppose if you have some claim to ownership of the furniture in question, like a reciept or something.  Then you could legally (I suppose) request to collect what is yours if they are not willing to pay for it.  Of course I am not a lawyer.

Marks resulting from "normal usage" are acceptable. You are responsible to fill in any holes but not to repaint them. You might need to cover the marks that you mentionned if they are very visible - sometimes an eraser is enough, or a small amount of paint only in those areas if applicable. Your offer to repaint the entire room is more than generous and it should stop any claims. Take pictures if you can to have some evidence in case this escalates.

You cannot enforce payment of your furniture unless you have a signed contract of some sort for that, otherwise either the new tenant accepts to pay or you take it away.

If you have already left the flat and in your opinion it was in good condition and no deposit has been lodged - do you actually need to do anything?

If it is a case of the other sharers trying to avoid paying for the furniture you left behind, then you have to calculate the value of the furniture against the cost of repainting the room - but before you repaint make sure you have the money for the furniture otherwise you could repaint and still receive nothing.

It also difficult to find a matching paint unless you know exactly what was used originally