Entity framework could care less whether you set the other direction or not, it will still save it correctly. However, when using your domain model, you may want access to both navigation properties right away. This requires setting the property as you are doing. The solution I use for nearly all navigation collections is the following
public class Family
{
public Family()
{
this.FamilyMembers = new List<Person>();
}
public IEnumerable<Person> FamilyMembers {get; protected set;}
public void AddFamilyMember(Person person)
{
this.FamilyMembers.Add(person);
person.Family = this;
}
}