Single axle vs Twin axle or SA vs TA.
The number of axles does not denote the size of the caravan. It is generally the case that TA tend to be bigger caravans, but there are some very big SA caravans that go against that premise.
The jury is out on whether TA's are more stable than SA's when towing. You will get reports from owners of both who will disagree about which is best, if indeed the number of axles actually makes any significant difference. Which ever you go for, good towing is about setting up your outfit properly, taking care about loading and getting the best nose weight. Remember there is no guarantee about good towing, and some combinations may just never work but these are few and far between.
One contributor claims they are easier to reverse. The difficulty of reversing or how quickly a caravan will start to go offline when reversing, is determined by the distance from the tow hitch to the effective turning axle of the trailer. The bigger the distance the slower the trailer will react when reversing. Again this has little to do with the number of axles, but from the point one above TA's tend to be longer but the longer any caravan is the slower (OR easier) it will be to reverse. It's worth taking some towing tuition to show you how to reverse a trailer.
As for choice of tow vehicle, that is really a personal matter, but there are plenty of vehicles out there that can tow the caravans you mention. You dont even have to necessarily consider 4x4's. Ideally you need to choose your particular caravan, then based on its MTPLM choose a tow vehicle whose maximum braked towing capacity exceeds the caravans MTPLM, and preferably has a Mass in Running Order that is at least 15% more than the MTPLM.
This will bring you in line with the industry guidance of a tow ratio of about 85% - which is only guidance and a few percent either way is not a deal breaker.
One thing you haven't told us is whether your driving license allows to you tow these outfits. If you do not have cat BE or B+e on your license categories, all the outfits you are considering are beyond your maximum combine allowance of 3500kg. - check your license.