Well worth borrowing a peak recording clamp meter, fitting around one of the meter tails and seeing how much power the house actually uses, ideally reading it and resetting it at the end of the day, after all meals have been cooked, and again first thing in the morning, before breakfast has been cooked (for those that have a cooked breakfast).
My guess is that many people will be surprised at just how much headroom they have available. I lived in a house with a 40 A main fuse for a few years (it was on a looped supply feeding a terrace of three houses) and didn't come close to ever using 40 A.. Also worth noting that it is perfectly safe to draw up to the maximum rating of the supply indefinitely, if push comes to shove. It's not exactly recommended, as the DNO applies diversity to the LV network, using the assumption that no house will always draw the full rated current, but it is safe. A 100 main fuse will take several hours to rupture if run at 150 A, and the incoming supply cable is rated for 158 A usually (if it's the very common 35mm² aluminium core, copper sheath, concentric cable). Even at 200 A it will take ten minutes of so to blow a 100 A BS1361 main fuse. I'm not suggesting anyone does this, just pointing out that there is a pretty hefty safe margin built in to the distribution network.
Lots of good input above, but I would whole-heartedly say that 2 x 16A EVSEs* is a terrible idea. If you have to upgrade the cable then so be it, it sounds like you can do that reasonably easily. However, worst case just stick with the single 32A EVSE and swap the car locations (or get a really long cable). That would *still* be better than 2 x 16A EVSEs, in my humble opinion.
*Sorry for the pedantic use of the acronym EVSE (Electric Vehicle Supply Equipment), but there seem to be a few members who get upset if one uses the word "charger" (a very common-use word that everyone understands, but hey-ho).
I agree wholeheartedly, charging at just 16 A is a PITA at the best of times, and as most of the cost is in the labour involved, it seems daft not to provide for 32 A charge points - the cost is likely to be under £20 extra, for a worst case. FWIW, I agree with using EVSE, or charge point, primarily because it removes confusion. A discussion that uses "charger", when referring to AC charging, refers to the units fitted under the rear seat of the Model 3, that are the actual battery chargers that deliver regulated DC to the battery pack, in much the same way as a phone charger delivers regulated DC to a phone battery. An EVSE/charge point is just a power outlet, calling it a charger is like calling an extension lead running a phone charger a charger, or calling a kettle lead a charger, it makes little sense.