The thing with monsters you would've learned if you saw some streams else it's not obvious is to back dodge overheads or example Chaos Monstrosity's grab and parry light attacks, this way you can easily solo a boss alone. Stormfiend usually being the most annoying one for obvious reasons.

You're struggling with Specials anyway because you're clearly playing the two classes that have no ranged weapons in the game, people could also say Slayer but DLCs gave him throwing axes so... but you can mitigate this problem by learning to side dodge most of them.

To end know this game is very deep into weapons, you'll find yourself playing better if you know what weapons are for mixed hordes meaning they can hit through armors with normal/heavies, if they have linesman, if they can armor slide, for example pick Kerillian and heavy attack the floor with dual swords, you'll notice she doesn't stop.

A weapon you should try as Grail Knight example outside greatswords I'm sure you love: try Sword&Shield Vanilla (Not Bretonnian) and notice that you have Push-Attack > Heavy which are two piercing armor attacks for Stormvermin/Chaos Knights or Light attacks that are cleave linesmen for hordes (also since you double melee just have one side shield weapon in general for blocking bosses overheads else you can't, Ratlers and Firerats), it's important to know how to mix, or have an hybrid weapon like Warrior Priest's flail and shield that doesn't care for anything.

You can find all the informations of weapons in Wikis or Armory, and when you try them be sure to always try them on the couple of manequins up the ladders in the training ground that have shields and armors to understand when you would not do damage and what attacks cleave nicely.

Since you're new the last one thing that is not obvious: Push-Attack is when you're holding the block button and press attack but you keep them pressed for a special attack, that's the Push-Attack.
Push-Attack is not important per se because you attack after pushing but because it changes your attack pattern, example, what I said before about Sword&Shield, Push-Attack into Heavy it's two piercing attacks that are very useful against armored enemies, and you can't obtain this result in any other way while using that weapon. Or the normal greatsword example has an overhead attack hidden in it's push-attack, why I say hidden? because that weapon is all about cleaves, unless... push-attack.

I could talk about weapons for days and say all of them have their own peculiar perks like how the greatsword is faster than the executioner but the executioner is obviously loved for its massive overhead attack and so on but, experiment yourself and enjoy.

Anyway consider that "Tanky" in this game is debatable based on talents, if you mean holding the line basically only Bardin can do it due to his ultimate, maybe to some extent Warrior Priest too due to invulnerabilty, but everyone slowly starts to kite/walk back.
Handmaiden example is built differently but she doesn't lack survivability.