If the loan needs a guarantor, you can ask for one. You can't tell the borrower who to ask, though. If the borrower's mother volunteers, that's fine. I'd get intent from her as well.
The cite you have refers to loans to a corporation. Banks can require insiders/shareholders of companies to guarantee loans when the borrower is the business. But that doesn't really apply here since your loan is to individuals, not a business.
ETA: KB beat me to it!