To begin with, thank you for such a detailed and professional review! We really appreciate it.
Firstly, the place indeed doesn't look like your ordinary historically accurate village. On the second thought, some parts of Kievan Rus at that time were located in places unfavorable for cultivation. Therefore people were engaged not only in farming, but in fur trade. That's the reason why the village is located in a dense forest. Although, we forgot to depict fur trading and other stuff in the game, haha :)
The game came out completely linear due to the lack of time I guess. The dialogues were written 3 hours before the deadline, so all of them are clunky. The whole plot was thought up superficially beforehand but there was little time to fill it with rich content. That's the biggest flaw in my opinion. Another flaw is the dialogue system mechanic. It is weird :) We wanted it to be like one in Skyrim, but there were issues with the player camera rotating around chaotically when talking to NPCs just an hour before the deadline. So we had to do something and now we have what we have. There should have been an option to skip Intro and Outro, but we had other important things to implement first.
In terms of history, I have the same thoughts as you. The game portrays Mongols as the highest evil. However, I dislike such approach where there are the good guys and the bad ones. I think, in essence there are always the lesser of two evils. In the end, it is the common folk who gets beaten the most. I really like stories where you see the whole picture and can choose sides. Although, as I mentioned above we failed to manage our time properly to concentrate on a plot and characters.
As for the last question, we've used Western sources to show Mongols as a global threat which everyone had heard of at the time. It is not just Mongols and Russians fighting. We wanted our game to be Western oriented, so players could be like, "Hey, I'm from Hungary/Poland. Did the Mongols actually reached these lands? Did they really were so powerful?". Unfortunately, I haven't stumbled on Galician-Volhynian Chronicle. I thought of using other chronicles, but they were heavily influenced with religion themes and it was quite hard to extract a good story out of it in comparison with Western sources.