Nope, no cheats or mods. I just start the game normally, get money from horse quest, marry, rescue brother, build party, but instead of ransoming the lords I attack, I execute them on the spot, 1 faction at a time, sparring only 1 per faction. Once I have the perks keen sight and mounted patrols (via normal gameplay, like every other playthrough)I will hold these rulers in my party until I have them all. This important because if you finish a faction pre-maturely the land goes to another faction which will let rebellions pop all over thier foreign land, they have almost zero competence at maintaining fiefs if they get a bunch at once like that.
Why? I'm faster and more powerful with a full KG party and scouting perks, I never have to fight anyone I don't want to. Think they stay in 1k+ armies forever? Think 100 KG can't each kill 10 enemies if they really had to anyways (they can)? I did it last May too without KG and just heavy HA. Even in games where I don't kill them I still hunt them down and keep the entire faction prisoner while I take thier fiefs 1 by1 with just my 1 party..... I mean who can stop me they're all in my prisoners.
Nope, Bannerlord difficulty! Native! If you can beat an average Lord party you can do this (maybe not as fast and easily), you're just defeating and killing lords until their aren't any. Nobody makes you fight an army (though you can and I do), you can always hunt elsewhere and wait for it to split up.