The question has been asked "when and what is the correct way to bring doubles?"...
Most people think they should stop driving on their cattle when they have doubles and that is INCORRECT. You have to drive on the cow you need first.
As you become a more accomplished sorter you can set doubles up.
Until then when doubles start to form still ride to drive the cow you need out first. If the other follows Great if not you've set a duck up for your partner.