What is the Shariah ruling on the inability to release the guarantee for a colleague who is still benefiting from an interest-based bank loan, after settling one's personal loan and having the colleague's guarantee released?

It is impermissible for a Muslim to borrow with interest (riba), nor is it permissible to guarantee someone who borrows with it. This is because usury is among the gravest of prohibitions, and the Prophet, peace and blessings be upon him, cursed the one who consumes it, the one who feeds it, its scribe, and its two witnesses. It is also impermissible for the guarantor to take a fee for the guarantee or to derive any benefit for himself from it, because he is obligated to repay the debt, and the guarantee becomes like a loan for which no compensation may be taken. Therefore, it is impermissible for the bank to stipulate that each person guarantees the other in order to grant the loan, because this draws benefit for both of them. Your duty is to repent from this.