You chose:
Approach the top management (your grandparents) quietly and secretly. Explain what is happening with padding the expense accounts and suggest that they develop a plan as to how to change this prevailing practice.
After hearing from you about the padding practice among the salespersons and the Sales Manager, the top management felt shocked and outraged. Investigation of the expense accounts showed that the practice was wide-spread. They are anxious to take immediate punitive action against the sales personnel and the manager. However, you believe this is both unwise for the performance of the firm and will lead to great hostility towards you as the whistle-blower. You feel that you need to defuse the situation.
You explain to your grandparents that since the practice is so widespread and entrenched, the sales personnel probably don't perceive it as unethical at this point. They will strongly resent any punitive action and this may have an adverse affect on sales revenue for the firm. It is in their best interests to look for root causes, such as below standard compensation, and introduce a plan to modify their behaviour that includes rewards as well as punishments for continuing the behaviour.
Believing that your grandparents will not be easily dissuaded from taking punitive action, you explain to them that if they do that, you will have to leave your sales position.
You return to the sales manager and say that you have reported the padding to top management and he had better take action soon. To back up your position, you admit that you are the granddaughter of the owners.