Definitely RiverClan. But I do like knowing the families as well.
In RC we don't have parents for Mosspelt, Icewing, Duskfur, Shimmerpelt, Lizardtail and Havenpelt.
We don't have fathers for:
Willowshine (Mosspelt is the mother)
Minnowtail (Dawnflower is the mother)
Mallownose and Sneezecloud (Graymist is the mother)
Curlfeather and Podlight (Duskfur is the mother)
Graykit, Mistkit and Frostkit (Curlfeather is the mother)
Cats with confirmed both parents:
Mistystar (Bluestar and Oakheart)
Mothwing (Tigerstar and Sasha)
Brackenpelt, Jayclaw and Owlnose (Petalfur and Mallownose)
Nightsky and Breezeheart (Icewing and Mintfur)
Softpelt, Dappletuft, Gorseclaw, Harelight (Lakeheart and Lizardtail)
Fogpaw and Splashpaw (Havenpelt and Sneezecloud)
Reedwhisker's father might be Blackclaw if this is still canon. Mistystar is Reedwhisker's mother.
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In WC we don't have parents for Gorsetail, Nightcloud, Leaftail, Emberfoot, Harestar, Kestrelflight, Whiskernose, Crouchfoot, Slightfoot, Oatclaw and Hootwhisker. Larkwing is a complicated issue.
Cats with both parents confirmed:
Crowfeather (Ashfoot and Deadfoot)
Heathertail (possibly Onestar and Whitetail, at the very least CT heavily implied Onestar as her father)
Breezepelt (Nightcloud and Crowfeather)
Sedgewhisker (Gorsetail and possibly Beechfur if this is still canon)
Featherpelt and Fernstripe (Sedgewhisker and Emberfoot, two litters) - Larkwing might also Sedge and Ember's daughter, but, like I said, it's complicated.
Brindlewing, Smokehaze, Applepaw and Woodpaw (Heathertail and Breezepelt, two litters)
Whistlepaw, Songpaw and Flutterpaw (Featherpelt and Oatclaw)