Varroa jacobsoni mates in the capped cells with the pupae. The mother mite
enters the cell just before it is capped and immediately goes to the bottom
of the cell and feeds on the worker or drone jelly. Then moves up and feeds
on the prepupa. Then 60 hours after capping the female lays her first egg,
generally a male, then subsequent eggs laid are female. They hatch and mate
before the bee is ready to hatch. So the mating is definitely sister/brother.