Can I legally take over someone's car instalments?

Not informally. The credit agreement stays in their name unless the bank formally substitutes the account holder, which is rare.

What is the safer alternative?

A rental agreement in your own name. You choose the car, the agreement is yours, and ownership passes to you at the end of the term.

Most applications are answered within 24 hours, with a 90% approval rate on complete applications.

Taking over someone's car instalments vs rent to own in South Africa: whose name the agreement is in, repossession risk, insurance and ownership.