Wielding is sort of nebulous in PF, but lets assume wielding means you have to be able to actively attack with it, not just holding it.
So supposing a class feature requires you to "wield" a specific weapon and that weapon is unarmed strike, does this mean these features apply even if your hands are full with other weapons? Even if you don't attack with unarmed strike that round?
Well, no. According to Unarmed Attacks if you have certain feats or class features you can be considered 'armed'. That isn't the same as wielding a weapon.
This would go a lot smoother if you just gave a concrete example of what you are thinking so we can actually look at what you really want to ask instead of hypotheticals.
I fail to see how the total defense actual even slightly applies here. It requires no wielding of anything and adds a dodge bonus.
I would say if you're wielding weapons you're not "wielding unarmed" as well.
According to the FAQ, you must make an attack roll to use a defending weapon. But with the total defence action you make no attack rolls so cannot use a defending weapon to defend yourself. That just feels wrong.
Two weapon fighting with sword and fist, monk with a longspear for reach and unarmed strike for close combat are both valid cases of wielding a weapon and unarmed strike simultaneously.
Wielding is nebulous, but in most cases, it requires to actively use the item, not simply having it ready.
Hugo example of a defending weapon is a particular situation where you actively use a weapon even if you don't make an attack roll. But from there arguing that the FAQ is wrong is excessive.
Especially the second example he made, as you can't use at the same time a longspear (a two-handed weapon) and an unarmed strike.
You either use one or the other.