But....

You say "but is says at Genesis 6:2 that they took to themselves wives, all whom they chose".

But it really does not say wives definitively.  The word "wives" here which naturally means cohabiting can mean "female humans" which does not necessarily mean cohabitation.  I think it means "to take over".  We see it many times and it is warned about.
2 Timothy 3:6 out of this sort are for those who enter into the houses and lead captive weak women burdened with sin (or guilt) led away by various desires.
Luke 22:3 Satan entered Judas
Acts 5:3 what is the reason why Satan did fill your heart?
1 Samuel 18:10 the next day an evil spirit from god came forcibly on  Saul 

"on Saul" has the same meaning as
"to the women" at Genesis 6:4

Now what about "all whom they chose"?  I will propose it means not the choosing of the angels.  I think it means all the women who chose the wayward way.  The word translated they can mean which.  It is an indefinite pronoun.  "All which chose" means the women chose.  They did not chose to "sleep" with angels. They chose to allow the bad angels to lead them just like the weak women burdened down allows men, and not God, to lead them.  (2 Timothy 3:6)  Matthew 24:37

By the way, why is sex called sleep?