How should one deal with people who were helped with money from an interest-based loan after repentance?

You must hasten to repent to Allah from the usurious loan. If you are able not to pay back the interest, then do not pay it back. Hasten to pay off the loan if doing so would lead to the waiver of interest; otherwise, do not hasten the payment. As for your relatives whom you helped, they have no connection to your repentance, for the sin of the usurious loan rests solely with the borrower.