2. Mold is a living organism. The only way to clean it is to kill them.
How you clean it depends on your exact situation.
3. It sounds the situation was discovered after the first repair was completed.
In that case, even it is correct to assume mold is the result of the leakage, the failure of the owner of the affected property to raise issues will bar that owner from recovering (as that owner has to bear some responsibility for the failure to discover).
So the owner of the affected property will have to pay for the second repair.