On the subject of monster families, I imagine Like-likes and pikkits are related to chuchus, zols, bits+bots, buzz blobs and other skins enemies.
Honestly, I imagined Likes of all varieties were their own thing. But now I think I wanna be mean to them for fun-- LikeLikes (and Pikits) are a variety of cursed undead.
They are Hyruleans who were consumed with their greed, to the point they became nothing but a giant sucking blob of flesh and teeth that steals from others. This is why there's so many underwater at night in the Great Bay where piracy is known to be so prevalent, why RupeeLikes are initially buried except for their lures until they find a victim, and why the ones in TotK hide in caves away from the sunlight that can burn them. Pikits are ones cursed by the Dark World. Also, while not a monster, Rupoors are afflicted by the same sort of cursed magic.
This does not apply to Deku Likes, which are part of the Deku Kingdom.
More headcanons about monster clans here.