Thank you for explaining a bit more about your situation and your present car.
The need for three (proper seats) in the rear is clearly a major factor, and as others have said it does point more towards larger vehicles. Again I would suggest you do look at the MPV's like the Galaxy etc. as these do have three proper seats and two more behind with ISO fix and you should find they provide more than ample space for a growing family. or luggage when on holiday.
Just a couple of points regarding your present Kia. according to this web site:-
I don't know how accurate these figures are, but they do seem reasonable, and it has set alarm bells ringing.
The stated Maximum Authorise Mass (MAM) for the Kia is 2110kg. You tell us your caravan has an "MPTLM (this is the MAM for the caravan) is just over 1600kg ". For the purpose of the driving licence entitlement "B" the wording is a Combined MAM not exceeding 3500kg. Using your figures your outfit has a combined mass of "just over 3710kg" On the basis of your comments I understand you only have entitlement B which means if you actually drove this outfit, you did so without having a valid licence.
Legally it is up to the driver to ensure they have the correct licence for any vehicle they drive, and you were remiss in not checking yourself, but I am appalled you were " told my car would tow the van ". The figures were easily accessible from the plates of both vehicles, and whoever offered the advice, should at least have alerted you to the fact you should have BE on their licence. If it was the dealer that told you then they have carelessly abused the position of trust of being expert in the field.
Secondly I will assume the Kia follow the common practice of setting the maximum towed weight limit based on the the cars GTW-GVW. The above website reports the limit is only 1500kg which would give the GTW a value of3610kg. As above, combining the weight plates show it has the outfit could have had a total weight of upto 3710, and that is 100kg above the vehicles stated limit. Unlike the Licence entitlement which uses the MAM figures, actuall overloading prosecutions can only be processed on the basis of measured weight, and if the caravan was empty of any personal items or luggage, it probably would have been within the cars GTW.
I do feel annoyed the dealer did not alert you to these issues.
You are correct the Kia is not suitable to tow this caravan legally, let alone trying to comply with the industry guidance.
With regards to comments about the B+E test possibly being shelved, don't hold your breath. Assume its not going to be dropped and continue with the training course and the test. If nothing else the training will cover several aspects of tow which will prove useful. If by some chance the law is changed before you take the test, then I'd strongly suggest to look up the availability of caravan towing courses offered by the caravanning clubs.