New family member and acceptance
The jealousy between brothers/sisters can't be avoided. It comes from the day the second child is born. It is a hard work for the parents to explain the first born child how much they love him but that they have to pay attention to the newborn child, too. There are so many tough moments, and we can't judge our children for their reactions to changings. But, also, our approach is very important, as the child sees the world through our eyes. Our goal is to keep their feelings safe and give them double love when a newborn comes into any family.
In theory, things are quite simple. Unfortunately, in practice, we fail to do things perfectly. Children are so sensitive and parents are humans, and there are so many issues coming out from the first day of living as a four member family (or more).