who where nami real parents? the town her mom ran from, she didn't even register nami in the officials records. so she hiding nami
then we got zoro, no info on parents, he was seen wondering around as a kid by himself challenging other.
We got Zoro's lineage on the SBS, pretty much the Shimotsuki who left Wano and ended up in the East Blue made the Shimotsuki Village
We have no idea whatever happened to Zoro's parents, but a kid being addicted with power and becoming a swordsman in an island full of wano trained fighters is a no brainer, and he is from the same lineage as Ryuma, i would just see it as inhereted will.
We really don't need info on Zoro's parents, anymore than we need info on Luffy's mom for example. They just didn't have a big impact on who they are now.
Nami would be interesting if they are special in anyway. But i actually just enjoy Nami being just another victim of that war, found, lost, and taken care of by her found mom. None of that information will change Nami's or Zoro's characters. So those informations really aren't needed.
Sanji's case was much more necessary, since we had a blank spot on his inferiority complex and his undying love for women. I feel like we have everything we need to understand the other Straw Hats right now...