Outcast's Path

1) Yes, the quests are given by peasants. If, by the time you take the quest, both villages are liberated for the Elves, the quest is immediately marked as completed (or at least it should be), and you receive reputation with the Elves. If not, you go to the village and talk to the peasants. In this case, the quests of the Humans and Elves are linked to each other.
2) According to my calculations, you can gain 65 reputation with the Humans without sacrificing reputation with the Orcs. Of course, for this, you need to destroy the Orcish units that would have joined you later. This is the price to pay for getting the bonuses at 100 reputation.
3) The console says that the hero Ellaine (or whatever his name is), who switches to your control with the Humans, is missing from the map, i.e., the script cannot find him, and the function stops working. Did you happen to lose this hero in one of the battles?
4) 50,000 is definitely a bug; the quest is completed twice, which shouldn't happen; there's an error in the script.
5) Yes, you would have 88 reputation, which means you missed 4 quests somewhere. If you can, send a screenshot with all the completed quests, and I'll tell you which ones were missed.

Added 1 hour 9 minutes ago
Reputation in the factions is also given for buying buildings (which cost 12,000).

While I was preparing the screenshot, I saw that the quest was completed. I was wrong: the bug was in something else - when the quest was completed, the Elf said that now I need to talk to the warlord, but I wasn't allowed to go to him...
But, having prepared the screenshot, I saw the red text in your message :eek:. So, the problem is this - of course, I didn't buy any buildings - my "native" army is now more than enough with the castle. But if I buy one, the reputation becomes 94. Is that it now? It's a pity that you don't get reputation for Goblin huts :)
Now, about the main thing - Ellaine, as well as all my other secondary heroes, is quietly sitting in his castle - I don't understand how you can lose a hero if no one is attacking. And the script error also calls the hero Nathaniel...
OH!
I took Ellaine out of the castle - the console changed the error message to "Object with name Peop1 not exist," but the cursor now points to the blue garrison in front of the northern castle! So, the problem was: after accepting the quest, all the secondary heroes are removed, and the program couldn't remove Ellaine from inside the castle. I'm going to try to go through it now...
Aha, I went through it... In the end, everything is as I expected: I met Laslo on the way, who can now come out and who blocked my path. Of course, there is no help from the Orcs on the bridge (I guess they will help when taking the empty castle), and I can't defeat this beast with his crazy army... In short, the situation is repeating itself from your previous map - you choose a light difficulty, you go on a light difficulty, and in the end, it turns out to be hardcore.
It's a pity...