Jamato,
I had my first US at 8weeks and saw 2 beanies and 2 beautiful strong heartbeats. Around 11 weeks I started feeling as if something was wrong and went in for a 2nd US at 11.5 weeks. At that time, Baby A no longer had a heartbeat. They figured, based on size, that Baby A's demise happened around 9.5-10 weeks.
At 8 weeks they measured 11mm and 14mm. I didn't realize at the time that the difference put us in the higher risk category for losing one of them. In fact, the doc said "oh, look at those great heartbeats. Well, you've beaten the odds and have less than a 4% chance of something going wrong." Now, from doing lots of reading, I realize that it occurs about 25% of the time when twins are detected before 10weeks and and even higher rate of miscarriage when they measure different sizes.
I did not experiencing any bleeding, just some low back pain and a little bit more clear vaginal discharge. Of course, this may be totally unrelated.
Baby A was still completely visible at my 13 wk US, so it is taking its sweet time being reabsorbed, but that's ok
You are lucky in the sense that you seem quite well informed and prepared for the worst. We can all still hope for the best. I was totally unprepared and quite shocked and devastated. It was quite a range of emotions that I went through. Now, I realize that nature did what was intended, and having 1 strong one left is certainly still a HUGE blessing.
-Julie