I believe that the parentage disappears due to the amount of coding required to keep it. (But who knows, they might be able to change that in future VV games.)
Many peeps keep a written record of their villages. You can find tracking sheets the Guides forums too. (Click here. This one is for VV3, but will give you the same idea.)

And there is a great thread (Anyone else get wee bit sad when a villager dies) for those of us who want to share our grief when our villagers pass away.