I don't remember the name of the armor so here's a pic XD
I use the sword two-handed. I'm level 70 and I'm also wearing Havel's ring.
That's the Gravelord Sword correct? Part of your problem might be that you are used to toxin doing a lot of damage for you, but The Four Kings are immune to toxin. Still, if the sword is properly upgraded it should be doing good base damage (but with crap scaling). What level is your sword?
Ultimately the best way to beat the Four Kings is to kill the first one before the second one can spawn, and repeat for all four. To do that, you are going to want to maximize your DPS in any way you can. So if you haven't already, level your sword to the max (or as high as you can with the materials you have). Unfortunately you cannot use any resins or enhancement spells to power up that particular weapon, but you could use the pyromancy "Power Within" to increase your damage output by 40%. Of course that also adds a health drain effect, so use at your own risk.
Alternately, you could change your weapon, but I don't know what your stats are, or what weapons you have leveled up. They are especially weak to fire, so a fire weapon or a Charcoal Pine Resin used on a normal weapon could do some serious damage. But using an underleveled weapon might negate any benefits of changing weapons.
I know I said I want to play this without a playthrough but I have a question. All this loot I'm picking up, armor, weapons and shit, does it have any point? Because I have a ton of nonsense stuffed in the bottomless box and I haven't found a way to deal with it yet.
There are not many pieces of equipment in this game that would be considered useless. Most of the weapons and armors will have a use to someone, but not necessarily you. A given player will only use a small fraction of the items that they come across in the game. But it's hard to know right away whether a given item will have some later use.
For example, different armors have different resistances, to the point where you might temporarily switch out your whole armor set for one with more fire resistance in order to fight enemies that use a lot of fire attacks. And while there are some armors that have straight up better resistances than others, their weight will prevent lighter characters from wearing them. Also, there are some armors that have high resistances, but you can't level them up, so they are really useful early on, but drop off in the late game where upgraded armors outclass them.
For weapons, it ultimately comes down to the moveset. You should try out different weapons that you pick up (not necessarily all of them), to get a feel for the different kind of movesets available. You may find that the weapons you are used to using are not necessarily the best for your playstyle. And while some weapons might have somewhat better stats than others, you can easily beat the game with pretty much any weapon in the game, provided the moveset suits you, and you keep it upgraded. There are a couple exceptions, like the Straight Sword Hilt you start the game with, but that actually has other uses.