Question Trip to South Africa

We are taking our 2 children (will be 4 1/2 and 20 months) to South Africa in the fall. I'm already stressing over what to do re carseats. We will be there a month and will be using a variety of different vehicles (hire car, family's car, cabs, etc). The kids are currently 40lb and 20lb and are in a graco nautilus and a radian rearfacing. I've looked into renting seats from a baby shop and that is possible but I have no idea what the seats will be like. The laws seem to be very lax/ non existent over there. I get the impression that rental cars are very small too. My current thought is to bring the radian and use it on the plane for the 4 year old (we won't have a seat for the 1 year old) and then using it for the 1 year old when we get there, rearfacing if possible. I'm not sure what to do about the 4 year old's seat though. I'm very nervous about checking his nautilus, plus it is so heavy and awkward. I'm wondering whether I should make my peace with him being in a booster for the trip and either rent one or bring one from here. My concern is that there may not always be a shoulder belt available to use. For what it's worth, he's a tall boy (maybe 42" now, not sure) so fitting him in a rented harnessed seat could be a challenge. Can anyone advise?

What do you know about the seatbelt situation there? I know in many other countries, where carseat safety is not as big concern, there are not seat belts in some cars. Just something to check into.

I would consider a Ride Safer Travel Vest for your 4 year old. They are great for traveling, as they fit in a carry on bag. They need to have a lap/shoulder belt OR a lap belt and Tether hook (but that may not be available in many cars in SA?) They also have no expiration date, so would be useful for a long time to come.

I have several of these, as we travel often, and I also have found they are great for a backup/emergency seat, or to send to a friends house with the kids.