One thing my last DM did that helped at high levels (also low levels, but especially high) was to split solos into, effectively, three monsters. So a dragon might become the head, the body, and the tail; while a demon might be head, body, and arms, depending on the powers. He would divide the solo's actions up and give each piece hitpoints so that two of the pieces were equivalent to an elite monster and the third was equivalent to a standard monster. Each piece gets its own initiative and set of standard/move/minor actions, and players target pieces separately (so, for example, an assassin could shroud the head, but wouldn't get shroud damage if he then attacked the body).
You would want to adjust the specific mechanics for your own game - we tended to address issues like whether "slowed" affects one piece or the whole creature on the spot and depending on how the creature was split up - but if your aim is to reduce complexity, it would be worth figuring out satisfactory answers to common effects up front. Then once play starts you already know the answer.
It ends up being significantly simpler for the DM since you have the strength and threat of three monsters, but the abilities and powers of only one to keep track of. It also requires fewer additional monsters/terrain/whatever to build out the encounter, again reducing the complexity of any given combat. You also get the advantage that a combat against a solo becomes much more interesting, because you've got three parts of the monster moving and acting independently (preventing the solo from being pinned down and focus-fired), which again increases the fun without increasing complexity.
Choose 1 of the following: Individualized Plot Decisions, 4th Ed Party Cohesion, Respect Characters Ideals1. At the end of the day, your system and your goals don't match up well.
You can:
- Present challenging decisions
- Prevent PC conflict
- Respect different ideas and ideals.
- Run a game designed for murderhobos to have colourable excuses to kill everything.
At the end of the day, your choices oppose each other and are not particularly compatible with the game system you've chosen. If you want to present choices that matter, they have to matter: PC conflict must be allowed as the losing side must be allowed to escalate (see Dogs in the Vineyard).
While the same page tool is useful here, it's important to begin by articulating your priority of desires. If you want to require group cohesion, set up narrative (and if you can) mechanical incentives for consensus. If you want to present challenging decisions, figure out your characters' motivations and pry at them. You may find that your game of D&D doesn't fulfill your requirements well. This is fine. There are hundreds of game systems out there, and one of them will fit better.
Fourth edition can certainly present morally complicated decisions, but doesn't fufill your requirements as the decisions exist purely in the narrative area of the game. Therefore, they're an excuse to frame different set-piece battles, not have the possibility for party-conflict.
The way to think about it is that 4e is like a big summer blockbuster. There's plot, and there are action sequences. The plot does an absolutely necessary job of tying the action sequences together and making us care about them. In "plot" time, there are very little rules and the protagonists can shout at each other as much as they want... so long as the issues are resolved (to a point where they can banter with each other about them during the fighting at least) by the next "set piece battle."
4e's rules focus on set piece battles between the party and monsters. This conflict is built deeply into the game (mainly due to different rules for monsters and PCs). This means that PCs cannot engage in PvP: there are no rules for it. While you can fake it, fparty-conflict has never worked when I've tried it, save when one person betrays the party, discards their character sheet, and that character becomes a boss-monster for the party to kill.
Note the assumptions there. Things that interact with the party, by definition, die. Good encounter design in 4e is to threaten the party with death without actually killing the party. Note also the protagonist is the party not the individual characters within the party. More so than in all the other D&D games, parties are cohesive groups by the mechanics, and not simply a bunch of fellow travellers.
If you don't want a game full of tactically interesting set piece battles connected by however much plot you're willing to provide and your group is willing to engage in, 4e is not for you. The party, as protagonist, can certainly make these ethically challenging decisions: they inform which battles are to come and what framing goes on in those battles. The PCs can influence the party's decision making process, but cannot defect from it save by defecting from the game.
1On a 10+ choose 2, On a miss, the MC gets to completely derail your campaign.
Best Answer
Over the years, social management systems in games like this have often seemed weaker to me than other parts of a game. SoIFRP has a fairly robust system, though which I find if you treat it like combat can have good results no matter the disparity between 'levels' of the participants in an Intrigue.
A key point I find useful to remember is that in most cases involving dialogue and interaction, no one leaves unaffected. Keeping the human reaction to what is going on in the forefront of your mind as GM during each stage of the scene, whether it be manipulation, seduction, persuasion, intimidation or what-have-you, helps keep things on an even keel. By running the intrigue with the idea that at the very least they will walk away from this with something to say about their opponent's statements or reaction ("What an idiot!" or "How clever!" and so on) no matter the outcome, they will always have some weight.
In the specific case you present, the characters are highly adept at this sort of thing and should be rightly feared as persuasive men and women. As the GM, you have discovered that they can get what they want from people easily. The challenge doesn't really lie in letting them use these abilities or in changing the system to reduce their effectiveness, it lies in making the use of them interesting for everyone and allowing the NPCs to react as they would.
Suggestions:
Ultimately, as it states in the question, the PCs were designed to be social intrigue powerhouses. The game will have to allow them to be so, but it does not have to just lie down and take whatever they dish out. Use the system to challenge them, extract conditions and leverage from them, have the NPCs react naturally, band together, and seek help, and remember with sharp detail all the promises they have heard before.