I'll chip in here on the most recent point. I'll apologise in advance as I'm unaware of any specific mods, but I think I may know the answer to why the AI is more passive against in a multiplayer game than in a single player game. War weariness is disabled in multiplayer for some reason.
In vanilla settings, this means the AI has a lot less reason to shift out of Democracy or Republic in multiplayer, so it is more likely to avoid the incredibly high unit numbers of say Fascism that invariably lead to the AI getting itself stuck in a more militaristic government (for cheap unit support).
Whereas in single player, War Weariness pushes the AI out of Democracy or Republic and sends it into a cycle of staying in militaristic governments with more unit support.
The only solution I ever found was to nerf Democracy and Republic in multiplayer and buff the more militaristic governments. Primarily around unit support, but also around corruption. It is a very delicate balance and I ended up including two new government types (one medieval, one modern) that bridged the gap between the militaristic govts and those govts with the trade bonus. I did this by creating two governments with the trade bonus and better unit support than Rep & Dem, but with key failings in terms of xenophobia, corruption and whatever the setting was that limits culture growth in captured cities.
This creates a route for the AI to de-escalate its military out of the militaristic govt unit support trap, albeit a route that it rarely chooses to take. In reality the main benefit is that when a militaristic govt attacks a Rep or Dem, the Rep or Dem will usually have a revolution to one of my halfway house new govt types and may therefore manage to avoid entering the militaristic govt unit support trap itself and, once peace resumes, may revert to Rep or Dem.
If you felt this was the problem then to compliment the above I would suggest:
i) making anarchy for the AI longer but with less corruption (so they can still operate adequately during the likely higher number of revolutions caused by the above changes).
ii) increasing difficulty levels specifically for when the mod is played in multiplayer (preferably nothing to do with unit support as that would knock all of your governments out of kilter and the AI will end up almost always favouring one above all others). Cost factor is the easiest one to change. For example, make it -1 for all difficulty levels in multiplayer compared to single player. This will result on the AI, on average, having more units and feeling more confident (and therefore aggressive in terms of diplomacy and government type) relative to the humans in multiplayer than in single player. This will offset the pacifity caused by there being no war weariness.
Actually, you may even just want to try ii) above first if all you want is comparable aggression between single and multiplayer and you aren't bothered about the AI favouring less militaristic government types. It is a 5 minute job to change it and you may notice results that are to your liking.