| It's weird, yes. But there is an answer.
Go to Ephesians chapter 1 and it explains that we are Gods children (believers, not everyone) through adoption.
He has adopted us and we now take on His spiritual traits.
During the Patriarchal period, if the oldest son was adopted, he would still gain all rights to inheritance, throne, or whatever else a first son was entitled to.
In Lukes account, 3:23 makes it clear that Joseph is not His real Father. Luke also includes no women in his account of lineage.
Numbers 27:1 -31:1 explains the adoption order. |