A theme that's often explored is the clash of different worlds. The angels come from a very different world compared to the Winchesters. Their different values, beliefs, and ways of life often collide in these fanfics. This leads to some really engaging stories where they have to learn to understand and accept each other.
One popular 'angels adopt winchesters fanfic' is 'Heavenly Guardians'. It has an interesting plot where the angels not only adopt the Winchesters but also teach them some celestial powers in a very unique way.
Well, it's hard to say for sure without reading the fanfic. But Castiel is a very common choice as he has been so closely associated with Sam and Dean in the original series. There could also be some lesser - known angels that the author has created specifically for this fanfic. Maybe an angel that represents a different aspect of angelic society, like an angel in charge of angelic education or something, who takes a special interest in Sam and Dean.
It could be Castiel. He's a very popular angel in the Supernatural universe and often has a connection with Sam and Dean, so he might be one of the angels to adopt them in the fanfic.
It might involve the angels seeing the potential in the Winchester boys and deciding to adopt them into their own kind of family or group within the story. It could also explore how the boys' lives change as a result of being adopted by angels, perhaps they gain new powers or face different challenges related to the angelic world.
The fanfic 'angels adopt sam and dean' may have a plot where the angels see Sam and Dean as key players in a coming apocalypse or a major event in the supernatural realm. So, they take them under their wings. It could show the brothers learning new angelic magic or abilities. There may be a struggle between the angels' loyalty to heaven's commands and their growing attachment to Sam and Dean, which could lead to all kinds of interesting twists and turns in the story.
I'm not entirely sure as I haven't read it specifically. It could be a fanfic where angels in some way take on or interact with the Winchester brothers in a situation related to buying something. Maybe they are helping or hindering the Winchesters in a purchase that has some sort of significance in the Supernatural - themed world of the fanfic.
The main characters are the Winchester boys, who we know from the Supernatural series. They are likely to be in some sort of distress or situation that leads to the angels' adoption. The angels themselves are also main characters. Depending on the author's take, it could be a group of angels or a single, more prominent angel like Gabriel or Raphael, but Sam and Dean are definitely at the heart of the story.
I'm not sure specifically as there could be many different versions of such a fanfic. But generally, it might involve angels taking in Sam and Dean as kids and guiding them in a different way than in the original story, perhaps protecting them from other supernatural threats in a more angelic manner.
You could try searching on popular fanfic websites like Archive of Our Own or Fanfiction.net. Just type in the exact title 'angels adopt the winchester buys' in their search bars and see if it pops up.