Many things contribute to human behavior. Birth order only explains a small part. Here are some other factors that disrupt traditional birth order roles ...
Next we are going to explain some things that can affect the personality of children and people, and that is that the order of birth has more to do than you imagine. Do not lose detail because it will surprise you.
Gender
Being born first does not necessarily guarantee firstborn status. In some cultures, a boy can be treated as a firstborn, even when he has four older sisters, because he is the firstborn.
Age differences
Birth order effects are strongest when siblings are separated by two or four years. With large age gaps, siblings can act more like just children or firstborns. Siblings separated by less than two years are almost like twins.
When the siblings are close in age, there is a physical equality. It's hard to snatch the truck from your little brother when he's not so little.
Brother with special needs
When a child is born with special needs, younger siblings can take on the role of the firstborn.
The Twins
Twins often don't follow typical birth order roles. Most parents tend to be very fair and do not emphasize birth order, at least in Western nations. However, when twins are delivered vaginally, the firstborn is usually larger and the second has a higher risk of health problems. In these cases, parents may unconsciously treat the first twin more like a firstborn.
As you have seen, the birth order can affect the personality of your children ... but what is clear is that each one will have their own idiosyncrasies.