The dragons and snake thing is from a Korean folklore/myth. Wherein it is said that a snake can ascent into heaven and become a god/dragon once it cultivated for a long period of time, however, should a passerby/human saw the snake whilst it's ascending, it will drop back down and became a large snake instead.
The brothers might've been some kind of creatures attempting to "ascent" and it seems the youngest brother is "failing" the ritual (ig falling in love with the father?) dooming himself to be a snake.
I'm not exactly an expert in this area since I only know bits and pieces from reading a lot of Korean manhwa, though I do wish they provide more of an explanation on what's going on exactly
Anyways (lol) so from the looks of it, 2nd son wants the father, 3rd son wants the 4th son, 4th son also wants the father (and is apparently going through puberty even though he appears to be in his early 20s and is also an active participant in the ritual), and the 1st son is acting all mysterious "i'm off to go meditate in the woods alone" vibes, talking about snakes and dragons going through a hole (it's almost like it's a symbolic meaning of their ritual). Meanwhile the father seems to want the 4th son while seemingly put off by 2nd son's advances but has no qualms about the ritual at all (the greed!). This is what I've got from these AI translations. Story is a chaotic sexually charged mess but I'm here for it! Bring on the next chapter.