Since I haven't read 'the house on the borderland graphic novel', I can't say for sure who the main characters are. However, they could be people who have some connection to the borderland or the house. Maybe an explorer, a local resident, or someone who has a special mission related to the place.
In the 'alice in borderland visual novel', there is Ryohei Arisu who is a central character. Another important character is Yuzuha Usagi. She teams up with Arisu in many of the challenges in the borderland. There is also Chishiya Shuntaro, a rather intelligent and calculating character who uses his wits to survive the games.
However, across the other novels in the collection, there are a variety of characters. Some are adventurers, like those in certain stories who are exploring uncharted territories. They are often brave but also vulnerable to the strange and dangerous things they encounter.
Alice is definitely one of the most interesting characters. Her name is in the title for a reason. She is constantly adapting to the strange world she's in. Another interesting character is the Mad Hatter - like figure who has his own set of rules and motives that keep the story mysterious.
Arisu is definitely one of the most memorable. He's the protagonist and his journey of survival and self - discovery makes him stand out. Another is Usagi, she's strong and a great partner for Arisu.
Overall, Alice in Borderland is reasonably faithful to the manga. Some minor details might differ for the sake of the adaptation, but the core story remains intact. There are no major deviations that would change the essence of the original manga.