It depends. See your doctor.
The dead twin will be still-born and will have not effect on the remaining twin. You do need to speak to your OBY/GYN for more detailed advice.
Yes, that is very common.
That is what they call "vanishing twin" or "fetal resorption." Sometimes it is not fully absorbed, but flattened, and the condition is called fetus papyraceus. If this happens in the first trimester, there may be no other complications except some bleeding. However, if it happens later, it could threaten the health of the mother or surviving twin. If it happens at the very end, and the dead fetus is low-lying, then a caesarean may be required to deliver the living twin.
The fetus' umbilical cord. (Singular) The twin fetuses' mother. (Plural)
If you were to miscarry one twin the other fetus can still survive, but the chances for that are SLIM!!
Chances are, something happened to the twin. But since the remaining baby has lots of room to grow, it will probably be born as if it were a single.
It happens quite often. It is called the vanishing twin syndrom
In the books, Ali had a twin sister. The dead body the police found was her twin sister. Ali killed her sister and Ian.
A human being must be sexually mature to become pregnant. Sexual maturity occurs in early teenage years. So, no newborn can ever be "pregnant"! A twin in the mother's uterus would never be in its twin's uterus. In fact, each fetus has its own amniotic sac--a large bubble full of special fluid where a fetus grows.
dead office workers
Their dead. So no.
I hope you mean 4.2 "inches?" At 18 weeks a fetus should measure 5-6 inches in length. Due to twin fetus' the length could vary to smaller lengths. It seems to be close to the range indicated but a little on the small size.