I could not find any information about miscarriage of twins when I found out we had lost our second twin as well. The only story I heard was an email recieved from another MOMYS. She had miscarried twins and had passed tissue, thought that was it, then kept up some bleeding, and passed more tissue about a month later. She said she'd have done a D&C if she'd known it would be so prolonged.
A D&C was not an option for me - I have an incompentent cervix and I was afraid that forced dilation could make my cervix even worse, so I was determined to wait it out. If I'd known then what I know now, though, I'd have called my midwife friend to come to me as soon as I started bleeding heavily.
A few days after my miscarriage, in which I passed both babies about 30-40 minutes apart and bled extremely heavily needing medication to stop it, I had a talk with a different midwife. She said that she'd had a twin miscarriage as well. Her story was like my MOMYS friend - two episodes of tissue passage a few weeks apart. However, she said she'd had three cases of twin miscarriage in her practice. Coincidentally (?) those three mothers were the only cases of hemorraging in miscarriage she'd had in her practice as well.
This is all just observational, but if you are expecting multiples and miscarry, then you may want to call for help to stay with you immediately as soon as the heavier bleeding starts and make sure they have herbs or medicines to stop the bleeding if necessary.
BTW, I had no bleeding after the death of our first twin at 6 weeks. I had cramping the day before the ultrasound showing only one sac instead of the two we'd seen the week before. The cramping was not severe at all and stopped after a few hours. It did not affect my cervix. I understand from my midwife friends that you can have no bleeding/no cramping, bleeding/no cramping, cramping/no bleeding, passage of tissue or no passage of tissue if you miscarry one twin of a twin pregnancy.
When we miscarried finally, one of the babies (who died at 9-10 weeks) was in a complete sac and placenta, the other (who died at 5-6 weeks) had a broken sac and placenta. I am very glad we stayed at home and were able to see what our little ones had left behind when they went to heaven. It was so important to me to see clearly that there had been two of the precious little ones. We are planning to bury them at our family's lake house and I'm going to plant two trees there.