When you cosigned the loan, you agreed to be responsible for paying the debt. If you are not making the required payments according to the loan agreement, they can call you to attempt to collect the debt. Should you pay the loan off, you can collect from the borrower. If he does not pay you, you can sue him.
Retirement accounts are protected. You may unemployed now, but when you are working again, if they have obtained a deficiency judgment they will garnish your salary and seize your accounts. There are other factors to consider before filing for bankruptcy. You should talk to a local bankruptcy attorney.
You must list all your debt, including judgments when you file a Chapter 7 Bankruptcy Petition. By listing the judgments, they can no longer garnish your salary or seize your accounts. However, if you own real property, the judgment lien survives the bankrutpcy unless you file a motion to remove the lien while your bankruptcy case is pending. It is best to file before they obtain a judgment.
Adding the creditors to the matrix is only part of the amendment. You must also list the additional creditors on Schedule D, E or F. In addition you should look at the Local Rule 1009-1 to guide you. Make sure you serve the creditors as well. If you do it wrong, it will not count.
If the lien was obtained after you filed the Chapter 13, it must be removed as it violates the automatic stay. If the lien was obtained prior to the bankruptcy, you can file a motion to remove the lien. You should discuss this with your attorney.