You’re correct, seraphim are the ones with six wings; cherubim have four, and traditionally archangels, like common malakhim, have two, but so do higher-ranking angels such as Dominions.
Among the SPN lore and fandom, though, the lines between choirs somehow manages to be jagged and blurry all at once:
- Castiel, a self-described seraph, has always been depicted on-screen as having two wings, whereas in real world mythology he’d have six. However, he was mid-high-ranking, which is sort of a blend of Jewish and Christian angelic hierarchies (in the former, they’re fifth highest; in the latter, they’re at the top).
- Corollary 1: Prior to the S7 clarification that he’d been a commanding officer in Earth’s garrison and the S8 specification that he’s a seraph, a sizable portion of fandom portrayed him as nothing more than an upstart mal’akh.
- Corollary 2: Gnosticism’s description of seraphim based on a more literal treatment of the name is that of a flaming serpent or dragon.
- Most rank-and-file angels, presumably malakhim, have two wings, which does match up.
- Zachariah described himself as having “four faces, one of which is a lion,” so he was a cherub, and he did have four wings. However, he outranked the seraph Castiel, while seraphim outrank cherubim in Jewish and Christian lore (in the former they’re ninth of ten, in fact).
- Conversely, Uriel was originally a very closely-ranked subordinate to Castiel, though the four wings he left in ash when he died suggest he was a cherub too.
- Archangels aren’t all that special in real-world lore; they’re basically just the biggest, baddest malakhim, which compared to the Jewish ophanim or the Christian seraphim is still almost the bottom of the ladder. However, real-world lore names Michael and Gabriel as archangels, so when SPN chose to make them the chart-toppers they appear to have also run with the idea that more wings is a signifier of higher rank.
- Corollary: Lucifer’s hierarchical status in RW lore varies. Depending on the tradition or sect you might find him called an archangel, a cherub, the highest and most beloved of all angelkind, or an unremarkable mal’akh who got too big for his britches. This is further muddled by his conflation with the Talmudic archangel Samael, who in turn is described in Gnosticism as a serpent, which is closer to their description of seraphim, which in older lore had…six wings.*
Is your head spinning yet? ;)
*And on a completely self-serving note, this is exactly what led to some ridiculous wordplay in one of my fics.