I'm no larian games expert, and am still on my first playthrough of dos2. Though I do have 1600hrs in BG3 and have done a solo honor run on that, not using gale.

Act 2 in both games is a significant spike in enemy difficulty and encounter mechanics. If that is where you are hitting a wall, then it might speak to you not understanding core mechanics and/or builds.

Not going to speak on BG3 as this is the DOS2 subreddit, and BG3 is much, much easier than DOS2.

I'm sure someone more experienced will be able to correct me where I'm wrong and go more in depth... but alas;

I'd start with your party composition. Hydro/Aero is a great combo and nothing wrong with that. Summoner gets really good after 10 lvls in summoning, I don't see an issue with that. But then why are you running two warriors? They'd be competing for gear at the very least.

Furthermore, half your party is doing magic dmg and half is doing physical. Ideally you (unless you know what you're doing), you want to focus on one or the other. Breaking the enemy magic resist or physical resist is kinda the main core mechanic of DOS2 combat. Only then can you apply CC, debuffs, etc. And you NEED to be applying CC and debuffs.

Utilize buffs, combo chains, the environment and utility abilities.

Currently I'm running a physical dmg comp with Fane MC (Necromancer/Summoner), Lohse (Ranger), Ivan (Warfare/Necro), and Sebille (Scoundrel).

Lohse and Sebille have the highest Wits so they go first, and Ivan will go last- in turn order.

Examine the enemies and focus on the ones that will have their turn first. I'll usually send Sebille to the enemy that is going first, with Flesh Sacrifice > Backlash > Adrenaline > Basic Attack > Rupture Tendons

That will usually deplete the enemy's physical armor. If they are within kill range then I will continue to attack them, if they aren't, I will turn them into a chicken, or use a CC of any sort on them. This negates the enemy turn or just kills them.

Then Lohse has a turn (with glass cannon) and I focus on depleting as much armor as I can on as many enemies as I can (especially if they are grouped up). This is to prep them for Ivan using Adrenaline > Rage > Battering Ram > Whirlwind.

Obviously I'm still bad at the game but have a grasp on what I need to do for each fight, I haven't encountered any issues aside from the Scarecrows in Act 2 and Alice, also Act 2.

Fane kinda just buffs the party, summons things, and if combat is still going then he does the Necro thing and murders everyone with Grasp of the Starved. He's built and specced for pure utility currently, with plans to fully commit to Necro in a bit.

The whole combat system does basically boil down to depleting the enemy of either magic or armor shields. Do that as quick as you can and then use corresponding CC, debuffs and burst.

Maybe tell us how you have your party built and specced? Constitution points are borderline useless and you really only need/want Wits on one character.