I've been looking periodically this evening and ONLY found DOH-JNB availability in Business on 06OCT. Nothing with BA/IB. You can do LON-DOH to connect in with this on 05OCT or earlier if wanting to make a stopover out of it. Then just book using avios JNB-CPT for when you need to get down there after your safari.... Keep in mind many half decent safari lodges and bush camps don't recommend (or even allow) infants so you might want to investigate this side of things. Nothing inbound from CPT/JNB/DUR after the 11OCT for 7 days. Perhaps you could look at using the VS miles for the inbound JNB-LON (nothing direct from CPT). You can use these on Virgin or South African on a one-way basis. Full details here although you'd need to check such availability yourself. Remember SAA also fly into FRA/MUC as well as LHR so there may be some alternative options if LHR proves futile on what is an extremely in demand route. Then just add on a RFS from there back to LHR.