We compare the similarities of identical twins to fraternal twins. Genes play some role in the development of some traits. This may tell us why we resemble our parents and why we don't. We may be parents with children and some might be similar and some might be different. Parents need to realize that when they think they are brining up their children, children participate in that process.
Parents respond to their children.
It requires understanding spouses. Twins serve an important function for one another. Twins may be very close to their spouse but it will be a different relationship. Some spouses may not fully understand what it means to be a twin. Some twins marry other twins because they know what it is like to have a twin.