It is real money. It is his business where the money comes from, not yours.
It is part of his employment contract that he is paid in lieu of commission, and hence, he has used this money to live on - including pay the CS he owes every week.
This IS real money. Loan or not it his concern, they cannot take it back from you, that is just how it is. If he leaves the job then he is in debt to them, they can't ask for all the money back from the people he has paid it with - it would be like the bank asking the supermarket you do your weekly shopping at for the mortgage payments back if you default on your loan, itms.

Don't stress on that, where he gets the money and how he affords his children is HIS concern, not yours. Once he pays it to you, it is yours and nothing can change that, short of him OVERpaying the CS if the amount being paid is wrong or something.
HTH