They do but they can be funky. You can not in any way REQUIRE a weapon to be used 2 handed, best you can do is give negatives when not multigrasped.
How do I go about doing this?
As for making something use the two handed all the time regardless of user size I thin setting the two handed tag to 0 forces 2 handed.
Just tested it, didn't work.
About quote #2 it could be that it has changed but I hadn't seen any indication of it, but that's pretty much the only real way to make a weapon two handed regardless of size, other than possibly an absurdly large number there, which dosn't seem to be working if I recall your previous post right. Perhaps 10000000 is above the upper bounds allowable for the variable, try a number at about 200000, that should not be too huge but still be well above what you need. EDIT: Just checked, yea, while 0 used to work it appears to either be bugged or to have changed, sorry about that.
As for quote 1 you give the Two Handed raw value on the weapon a number higher than the maximum estimated size of the creature. Which on default creatures I guesstimate at about 150% the number for bodysize in the creature raws.
To test if a weapon is properly two handed the easiest way is to go into arena mode, create your critter you want armed only with the weapon, then manually control the creature. Drop the weapon and pick it up again, then check your inventory and see how it says you are holding your weapon. If it's only in one hand something is wrong, if it's 'multigrasp' it is properly a two handed weapon.
In dwarf mode, in case you are modifying a save raws for a fortress, you need to assign the weapon to a 'dwarf' and make sure they are not using a shield, another weapon, or a crutch, and all their limbs are functional. And if the weapon shows up in the dwarf's inventory with the words "multigrasp" it is two handed.
If all of that doesn't work here's an example raw of a weapon I know is two handed to non-herculean, normal sized creatures, perhaps something got messed up somehow. It should be two handed for most of your creatures, although the abnormally large and most muscular may be able to use it one handed
[ITEM_WEAPON:ITEM_WEAPON_SWORD_GREAT]
[NAME:greatsword:greatsword]
//DESCRIPTION:A very large, long sword designed primarily for anti-calvalry combat. Happens to work well on large monsters too.]
[SIZE:1000]
[SKILL:SWORD]
[TWO_HANDED:79000]
[MINIMUM_SIZE:62500]
[MATERIAL_SIZE:5]
[ATTACK:EDGE:100000:9000:hack:hacks:NO_SUB:1200]
[ATTACK:EDGE:100000:9000:slash:slashes:NO_SUB:1200]
[ATTACK:EDGE:100:4500:stab:stabs:NO_SUB:1000]
[ATTACK:BLUNT:100000:8000:slap:slaps:flat:1200]
[ATTACK:BLUNT:100:1000:strike:strikes:pommel:1000]