No offense meant, but from what you are describing, you are obviously new to the game and I'm guessing this is your first time.

Anyway, I've been playing MM7 for a long time, I'm always happy to help people get started. It can be a very easy game if you know what you are doing, on the other hand it can be near unfinishable if you screw up your party build. Critical mistake: I can tell from your description that you are most likely using the default party. The default party is complete rubbish.

Critical mistake: Dwarven Cleric
First, your cleric is a dwarf. This is a blunder on par with rolling a 1 in a d20 game. Many monsters are programmed to attack characters of a certain type(species/class/gender). Well, 1/3 of the monsters in the game are programmed to attack dwarves first, so this just means that your cleric will end up tanking (if you've ever played WoW or anything similar you will know this is bad news.

Critical mistake: rogues are a waste of a character slot
Next, thieves are deadweight - almost a waste of a character slot. Their main specialties are: Grandmaster dagger, rogue skills (primarily disarming traps), and grandmaster leather armor (+1 elemental resistance per skill point).
None of these are really useful. There's no reason to include a rogue in your party just for grandmaster dagger, because if you want a melee machine, then you just bring a Knight (who gets grandmaster armsmaster, +2 damage/attack bonus/attack speed per skillpoint). Disarm Trap isn't useful, especially in the late game, because everyone (even your mage) should have enough health at level 60-70 that you can just eat the damage from traps, alternately you can just Telekinesis them open. While elemental resistance from leather armor is nice, grandmaster protection from elements scales several times as quickly.

Critical mistake: you only have one healer
Yet another spectacular shortcoming of the default party... what do you do if your cleric gets KO'd? No one else on your party can heal - your only backup is to keep healing scrolls/potions on hand.

Knights lack utility:
I've never found knights in MM6-8 to be that useful - they are only good at health, melee combat, and item repair. Clerics can already do master level item repair. MM7 has no "tanking" unlike most MMOs - there's no way to make enemies target one of your characters, although I guess you could make a dwarven knight. Relying on melee combat alone is dangerous - there are a lot of enemies that prefer to fight at range, and some enemies are just plain dangerous in melee, especially if you're new. Some players use 2 knights in their party, but I find them to be way too inflexible to be useful

My advice:
Casters are hands-down the strongest characters, especially in the endgame. In particular, you really shouldn't need knights because of "shotgun spells" (Sparks, Poison Spray, Shrapmetal). Think about this: Incinerate does an extra 8 points of damage on average per skillpoint and costs 30 SP. Meanwhile, grandmaster level sparks does
+9 damage and grandmaster poison spray does +10.5 damage per skillpoint while costing almost nothing. An effective tactic is to get multiple master/grandmaster level elemental casters, equip them with sparks/poison spray, then charge at enemies and unload at melee range.

Usually I prefer a party with 2 mages, a druid, and a cleric. If you aren't comfortable with an all-caster party, I recommend an archer/druid/cleric/mage party.

You absolutely need a cleric and a mage in your party, otherwise certain aspects of the game become very inconvenient or difficult. Here's a list of some of the consequences.

No cleric:
-No power cure (no group healing except if you want to use Divine Intervention or Souldrinker)
-No grandmaster protection from magic - vulnerable to instant death/eradication
-No resurrection (can't recover from eradication short of divine intervention or resurrect scrolls)
-Time limits on every condition removal - grandmaster skill eliminats all time limits
-No access to the grandmaster mind control ability

No mage:
-No grandmaster town portal/beacon. This means that you can't portal with enemies nearby.
-No "1 hour of invisibility per skillpoint"
-No access to the best level of "shotgun spells"
-No starburst; weaker meteor shower If I remember properly, titans attack female characters first. Unfortunately the default party has both casters as females, so they will ignore your knight and rogue for the most part.

Here are my hints for clearing the titans with your current party.
-Fly around and avoid turn-based mode.
-Have grandmaster protection from magic on at all times. The red titans have a chance to cause instant death (no matter how much health you have)
-Absolutely do NOT melee titans, they can dump sparks on you for serious damage. Remember that hint I mentioned earlier on "shotgun spells"? Well, meleeing titans puts your entire party on the receiving end of one of those.
-Aggro (pull) every titan in a large area. Fly rings around them and they shouldn't be able to damage you.
-Wait until the titans are clustered in a small area, then run airstrikes on them with meteor shower. Easymode. Leveling up isn't the problem. I can wipe out the titans and devils with a level 50 party as long as there's a mage in it. Wipe out titans with meteor shower, wipe out devils with starburst, problem solved. Excuse my language, but wtf are you doing? Are you meleeing them on the ground? because you absolutely shouldn't be meleeing them on the ground. The safest way to wipe out the devils is to fly around and starburst them from the air. If you absolutely must melee them, hover just above the ground and have your knight "joust" them. Always keep moving.
Note that this isn't a problem when fighting them in their colony as meteor shower is outdoors only. There's nothing wrong with ranged combat, the problem is that the default party is piss-poor at ranged combat apart from your mage. Archers can shoot 2 arrows at a time while adding their skill to their arrow damage, plus they can nuke. Druids and mages are the best nukers in the game. If you take the dark path, clerics can nuke with dragon breath as well See above strategy on starburst airstrikes and jousting. Airstrikes outdoors and shotgun spells indoors. You're welcome.

The problem isn't your party (even though the default party is defective by design, it's very doable with just your mage and cleric (and 2 empty character slots). Land of the Giants is more like Land of the Airstrikes, because it's easymode if you know how to airstrike and incredibly painful otherwise.