My interpretation is the story is from uke pov and it seems it also show how the uke view his world. My theory is uke had fall out with father as a result his relationship with mother and sister also drifted apart. The family inheritance and his status as heir to the family company didn't mean much to him. Hence why scenes involving his family looks like insubstantial peripheral vision. On the other hand I think he carried this deep guilt towards the seme because when they both small (seme elementary kid, uke junior high) he pushed the seme and run without calling help/without making sure that he's alive. Hence why this scene is drawn clearly and repeatedly. And seme is a confusing, conflicting character is a mirror to uke confused, conflicted feelings towards seme. That's just my thought on it tho'.
There's a lot of subtlety in play in this story, probably because it involving traditional asian family dynamic. Whether readers like the story or not is up to each their own. But I honestly feel that the plot is pretty clear and doesn't need more detailed background to father, mother, sister, etc. The family inheritance drama supposed to be a blurry background anyway. Shown by how sensei didn't draw detailed expressions of the family. The focal point is seme and uke. Guilt, attraction, on uke part. And hate/vengeance, attraction on seme part. The plot itself is cliche but I personally like the subtler plot and dialogue. And how the mangaka didn't spoon fed the readers with every little details. A lot of the back story is implied and subtexts so readers can have different interpretations of the story.