1. Your mother has taken loan from others with the assurance to repay the same at agreed rate of interest.
2. She shall have to repay the loan with acceptable rate of interest as per the terms of the agreement if any.
3. Normally, such money lenders take promissory notes with assurance to pay the amount which is shown as more than the amount actually taken since future interest is also pre-added to it to legitimise the act of giving loan with interest.
4. For running money lending business, one shall have to take license from RBI.
5. To avoid the legal problem, such money lenders add interest and take pro.Notes as explained above.
6. The stand that since those people are not authorised to run money lending business commercially, your mother will escape her responsibility and liability to repay the loan taken by her is not correct legally.
7. It will be prudent on your part to settle the matter with those lenders amicably.