Running Multiple Criteria Count

Have list of employees and their dependents organized into the following columns:
Employee ID (unique to employee), Relationship Code (E=employee, S=Spouse, D=child), andBirthDate. Would like to add a column called Sequence Code which counts the family members (employee= 0, S=1, oldest D=2, next oldest D = 3, and so on).

Employee ID RelationshipCode BirthDate Sequence Code
100006641 E 2/5/75 0
100006641 S 1/2/75 1
100006641 D 3/9/89 2
100005555 E 2/5/77 0
100005555 D 1/2/89 2
100005555 D 3/9/88 1

Note that the list is sorted by Employee ID, but not Birthdate. Can this be done with a formula in the Sequence Code column? I really suck at VBA