The reason why Celestial Dragons take normal humans as wives
The Celestial Dragons take strong female or male character from general population as spouses to get capable offsprings
Then there will probably be a seperate camp for these kids where they are mold to be strong warrior, who’s sole propose in life is to defend the Holy Land, aka the God’s Knights. Probably under the guidance of the Gorosei.
There are probably a bunch of kids up there as someone like Charlos had 13 wives even though he is just 22.
Say he started taking wives after he turned 18 than Charlos would approximately take 3 wives a year than too he could easily get this 3 women pregnant. So Charlos as he is currently still has 10 kids.
So woman like Ginny or Boa Hancock are targeted because they’re beautiful and capable. Whose kids under proper training would easily become very strong.
The perfect example is Jewelery Bonney who has a Bounty of 320 million berries. Under proper guidance she could have probably become even stronger.