I did this trip on my own with my DS when he was 7 months and then flew again on my own with with my DD aged one and and DS and two. It was fine - people are very kind. Just take spare clothes for you and them, food, snacks, a favourite toy, milk if you aren't bf and usually you can can keep your pram until just before you board. I imagine the skycot will be too little my DS was clambering out and it looked really hazardous
Be aware that at Oliver Tambo they often say you will be able to get your pram back as soon as you step off the plane but they are notorious for making you fetch it from the luggage carousel. I made a huge fuss and a member of the cabin crew carried my hand luggage to the carousel where I picked up the pram be firm.
Also if your DC gets a bit mucky with food etc don't change them until it's really necessary I did this then DD vomited all over me and her and I had no clean things left.