That's pretty much all that can be said about dizygotic kind of twins, right.? Well, except there is also a somewhat different kind of fraternal twin situation, for which I can find no name except for the name of the uterine condition which can lead to this kind of twin births. This uterine condition is called uterine didelphys, UD, or double ueteri, in which it is posible to get pregnant in each uterus, at the same time or even at different times, and possible to deliver at widely-different times. Two uteri, each half the size of a regular uterus means that at 20 weeks, the baby can begin outgrowing its home. This condition can also result in a single pregnacy or multiples of more than two, dizygotic or monozygotic. Besides the complications caused by smaller uteri, these pregnacies are also at more risk due to higher risk of ectopic pregnancies, as well as labor obstructions caused by having two uteri.
That must be what happened to one of my mom's friends back in the late Fifties: she went into labor & produced two boys--one full-term, the other a 7-month premie.