The Trustee's duties are found in the Bankruptcy Code. If you need legal advice, contact your attorney. If you are unsure whether or not your question is of a legal nature, call your attorney first. For example, my parents loaned me some money before the bankruptcy. I didn't want to list them because I am embarrassed and don't want them to know this Chapter 13 is happening.
Nobody can pick and choose who gets listed.
If you forgot to list someone, that debt will probably not be discharged. However, it is not too late to add them. You can add creditors you forgot by amending your schedules. This requires a small fee to the bankruptcy court. If you forgot a creditor, be sure to inform your attorney at once.