The grandma was the leader of the opposite group that they belong and the orange hair girl is going to marry off to the cousin with the long black hair
(Just clarifying) She wasn't the opposite/opposing group. The grandma is the one that was giving out the construction contract to either taeju's group or the group that kidnapped euihyun (it's why they kidnapped him) or a third group that we don't see.
Seeing one of the granddaughters shows what kinda deal taeju's aunt and the grandma lady made though for sure. I wonder if we'll see more of the character ლ(´ڡ`ლ)
So the guy referring to chap 41 is the grandkid of someone? (i forgot her name) the one with the sister whose hair is red/orange?