I don't breed- but I do know that breeding twice in a year is too much for the dam. She needs time to recover physically between litters.
We brought a second yorkie in to the house when Rhett was just shy of 6 months. It took him all of a day to decide that it was his job to watch over her
. He would get down from the bed in the middle of the night and lay down by her crate if she cried - of course, that only lasted a few weeks before he decided that he wanted to go back to sleeping all night. I didn't find her crying to last any longer than Rhett did, so I don't believe she feels isolated at night.
Oh- Welcome to YT!