How can I unlock these scenes?
(also spoiler warning this goes into detail, I'll just and make a TL;DR for them all tho, and the reason i put red and green choices in bold is cause they massively affect the storyline of the characters involved. you prolly know but wanted to say anyway.)
TL;DR versions.
(also Gunnar's is rather short in both the TL;DR and more detailed one so it doesn't really need a TL;DR but I gave it one just cause lol)
Gunnar/MC, just spam his events from the literal beginning of the game and you'll get it.
Logan/Barrel, pick the red choice when talking to him about the bandit camp and after going to the bandit camp at night, then check Logan's house/the sawmill later.
Logan/Korg, stay on the save you chose the red option with Logan on and get to an event called Bareshade expansion, then pick the fair as your first option and do whats needed for it then do the first fair to get it along and also the second, then speak with Korg and he should have new stuff, tell him he should have fun with the redhead who asked him for sex at the fair when prompted, then just wander the fair and it has a random chance to appear.
Lizard bad ending, get the Acolytes and Lizardmen lust to a total of 10 and choose all the red choices in the curse of lust storyline, then rescue Othra's husband and let her take him into the cleansing water pool.
Gunnar and MC is at the very start during one of his sex scenes before unlocking the route to northcrest and on certain days. just agree to whatever he says in the beginning and you'll eventually get it.
Logan and Barrel has a couple requirements before you need to get to the part with that scene. starting with the red and Green choice for him that says "encourage" or "discourage". discourage will be green since it means he's not getting corrupted/has a romance and won't get turned into a super slut, red means he becomes a super slut with no romance options. so to get that scene, pick red and after a bit (can't remember if it's after beating scar or before, so try both.) go to the sawmill at night.
Logan and Korg has the same requirements as the scene for Logan and Barrel, but also quite a bit more. you need to progress the story of northcrest a good bit and have rescued Korg from Viccoria, afterwords you need to get him to like you a little more and also do an event called "Bareshade expansion", this one lets you create one of 3 things, a guard tower, a new house for you and other potential residents who may move to Bareshade and a fair. you need to pick the fair and do the first fair then explore the second time and talk to Korg after finishing the second one, he should have dialog about someone coming up to him and asking for sex, tell him he should and explore the 3rd fair to randomly see the scene.
Lizard bad ending.... just pick all the red choices when talking about the Lake and get the Acolytes and warriors lust to a total of 10, far as I'm aware you get the warriors by "offering them some relief" as much as you want but at a max of 7 and the Acolytes lust to 3 max from what I remember but it might be 4 and only through singular events. you need to eat out the first Acolyte outside the temple, let the nymph have her fun in the forest clearing then rescuing the priestess and I think there's one in the dark swamp where you let the warriors have fun then rescue her at well but I'm kinda fuzzy on if that actually is one but I'm pretty sure it is. also rescue the last acolyte from the warriors after having sex with them to let her go. after that unlock the corrupted lake from continuing the lizardtribe story and I think the witches to then get an amulet from either Othra or the witch to see in the dark (or don't it's been a minute and don't remember if a light source is required for the corrupted lake) then go into the corrupted lake and defeat Roushk to take him back to the temple and... witness what happens.
however I will warn you the lizard tribes bad ending locks you out of a lot of content later, and I believe only has 2 exclusive scenes so don't try to do anything after you get them and just reload a completely different save where you haven't done the bad end route so you can keep up with the updates and actually be able to play certain storylines.