Another one in the 'old' (though not oldest) is technically the House of Wessex (Cerdic). While in-game they only go back to Ecgberht of Wessex, the family line should actually continue back to King Cerdic of Wessex who died in 534. Of course Cerdic didn't spring out of thin air either, so depending on who you choose to believe his line goes back further still though unfortunately the lines given as far as I know all essentially end up with Bældæg son of Woden which well... 
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In game there are three surviving members in the 11th century, Eadgar the Ætheling, Margaret and Cristina. They're landless, so you either need to give them land, or push Eadgar's claim to England as an Earl. So they're playable after a fashion at least.
.In game there are three surviving members in the 11th century, Eadgar the Ætheling, Margaret and Cristina. They're landless, so you either need to give them land, or push Eadgar's claim to England as an Earl. So they're playable after a fashion at least.