Sorry, I didn't reply to the several posters who brought up the MK return sector MRUJNB.

At JNB, before I boarded my flight, I went to the MK ticket desk, and spoke to an extraordinarily intelligent and helpful agent. He called Mauritius while I waited, and in liaison with them, cancelled my wife and daughters' reservations but not ticket, so their tickets remain on hold and I can re-book at a one way JNBMRU, or a dummy return, or whatever, with the fare then being re-calculated and me paying the difference or receiving a refund. As the JNBMRU flight was much the more expensive sector when I booked, I am sure I will be able to get them to JNB for less than what I paid originally for the return.

To re-emphasise how helpful this MK ticket agent at JNB was, I had to dash to my flight as it was starting to get a bit tight, whilst he was still cancelling the reservations. He arranged for his colleague to bring a print out confirming what he had done to the gate. I'm not sure how they knew who I was, but the guy just approached me and gave me the printout without first asking my name! Now that's service!!