I'm going to skip around some as you're asking quite a few varied questions.
The same fat tire bike will be the best and the worst depending on the pressure you put into the tires. You DO want bigger tires and if you are genuinely riding on deep sand (which kinda seems unlikely) then 4" is where you start and go up from there, keeping tire pressure down low - subject to your body weight.
How to measure torque: The measurement is in Newton Meters (Nm) and bigger numbers are better. MAYBE more useful is the amperage of the controller if you can find out what it is. More amps = more torque so here again bigger numbers are better. Also: 20" wheels vs. 26" wheels - the smaller wheels deliver more torque via physics. Clear as mud so far? Sorry there's no simple formula and if there was, you would find that bike manufacturers obfuscate as much as possible to try and make that result more cloudy.
Insofar as torque or even motor performance is concerned: Forget about motor wattage. Its meaningless. All it tells you is how much raw current (punishment) the motor is rated to handle, and even then it makes no sense in terms of what is actually happening. I'll explain: Watt output is a function of battery voltage times controller amperage. So lets say you have a 48v battery... First of all that 48v battery is really 54.6v when it is charged fully. Got that? Next lets say you have a 20a controller (I am describing a Sondors Fold XS right now which actually has these specs). So... at full charge (and only at full charge) the Sondors' 750 watt hub motor puts out 54.6 * 20 = 1092 watts. That could easily be a 500w motor (earlier 'X' models had them) and both 500w and 750w motors deliver the exact same almost-1100w. The 750 is just beefier inside and if you hammered it forever on full throttle its far less likely to have a problem of some kind (but in all honesty neither of them is likely to have a problem). The wattage rating has nothing to do with actual output of power to the ground.
It seems more likely you would be on a paved path. At which point you can ride on much smaller tires. 3" tires would be fine on a paved path with sand strewn across it - even if that sand is an inch or two deep.
You say you are a plus-sized person. Bear in mind the bigger the tires, the greater their load capacity. Especially if they have been deflated some for traction, which is a requirement on deep sand.
By the way its common to carry along a battery powered pump to deflate and reinflate tires if you are riding on a path toward the beach. You ride there on road pressure, deflate, hit the sand and then reinflate for the drive home. Exactly the same process as if you are 4-wheeling in a truck.
I am a moderator on the Sondors Facebook group (don't work for them) and I see comparisons all the time. For what you want you should consider their Fold XS, which at 1799 is less than some of your other choices and delivers more - the company owner is a True Believer in ebikes as transportation and this influences his pricing strategy. The XS line was created after they looked at all the upgrade mods the users were showing off in the group and they made a bike line with those mods included from the factory.
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Max load on these bikes is listed at 300 lbs and thats a real number. The bikes are quite sturdy. That is a 'true' Bafang 750w motor core in this bike, and that means its the beefiest geared hub motor on the market. Its rated for 80Nm but if you pull the casing apart you'll see (thanks to the markings inside) Bafang proofs them at the factory to 100Nm. Basically, its a sturdy little bugger that is effectively indestructible. Also, the fact that Sondors actually tells you its a 20a controller is a step up over most manufacturers. They did not put in a 25a controller like the full sized XS simply because the smaller 20" wheels made the bike wheelie with that much torque.