I had a male and female yorkie that were a week apart. They always slept together... in fact if they weren't together they cried. We got them at 10 weeks old... so that is about the same age as yours. My guess is they will want to be together. It may take a little adjusting, but you will love having two!! Mine are so close and I have never had to worrry about leaving them when I need to run out.
But if you are getting a male and a female... be watchful in another couple of months they are sneaky when they want to "doggy pile". Mine even got to each other through a crate
