My IE Special Book Of Randomness

question #3

Hey everyone :dead , alive , sick , cool , and everyone in the world sitting in their room or on the couches because of what is  named quarantine!!!
Today is a new chapter baby(s) or dear (s) if you were adults .looooool

And today's question is
*drums*
*drums*
*drums*
*More drums* (cuz I didn't find a drums emoji pfft )

And after a long intro so I can make my chapter longer here we go

Q: how come endou mamoru have the name endou?
I know this sounds stupid but I will explain everything in a moment :

Well you see , endou mamoru's grandfather : endou daisuke is his mother's father (sorry but Idk how to say this in English since it's not my mother language) so his mother must be endou though his father is endou too.

So my theory is :
1/ endou's mother and father are cousins since his father knows about his wife's past with daisuke as shown in ep 5 from the original series
Or
2/ this is a mistake made by the mangaka or the animists .
Or
3/ idk really maybe it is a Japan's thing or even a religious one .

So that is it minna sorry for the really short and unimportant chapter but hey isn't it a great and genius question??lol
Sorry.
Anyway plz tell me your opinion about this question or theories in the comments !
Keep your standards low and keep ion reading my book and giving me vorptes for nothing
Byyyeeee