I have no idea as answers for your questions...

But when DD2 was born she was the loudest sleeper ever! And she still is..
At first we would laugh at the nosies she made, but then I used the noises to give me some peace of mind. I knew that whilst she was making those noises I knew she was ok. She snores, she mutters, makes the weirdest noises and generally has no idea what the term 'quiet' means when sleeping.
After 20mnths of getting used to this, I dont even need to walk into her room to check on her, mostly we head down the hallway til we can hear her snoring, turn around and go back to what we are doing.
Although I think snoring is contagious... DD1 now snores too!! And they share a room together, the noise that comes from that room every night is hilarious!