My two little Yorkies are 2 and 3 yrs.old and are (for the most part) housetrained. Except for during the middle of the night, one or both??

will have an accident somewhere in the house. I have always had dogs (although these are my first Yorkies)

and every one of them has awakened me by getting in my face, kissing, whining ,something, IF they needed to go out in the middle of the night. But not these two. I've tried everything. They sleep in the bedroom with us...I tried closing the door...they just go in the bedroom. I've even been awake and heard and caught them and taken them outside immediately. They go out at about 11:00 pm every night and out at between 6:00-7:30 in the morning. For the most part this isn't a huge issue and it's not like it happens EVERY night...I'm just perplexed as to how to "train" them to wake me up. As I said earlier, my other babies just "knew" to do it. I'm a quasi light sleeper and it wouldn't take much for them to wake me. They scratch the back door when they want out during the day...but they don't bother at night. A few weeks ago...I put bells on the back door to hear IF they would scratch...I was awake and heard my little girl Brockty, jump off the bed and tear down the hall. She went nowhere near the back door, but peed in the livingroom instead.

Strange little furballs. Other than this and a few other minor quirks

...they are perfect little angels. Any ideas?