The foreign key between two children in the same hierarchy

It is a one to many from the "Children" table; one child to many staff, one child to one or more "ResponsibleAdults" (who could be any familial relationship). If you change Father & Mother fields to be Responsible1, Responsible2 and add Responsible1Relationship, Responsible2Relationship to "Children", you'll solve that problem. Alternatively, you can create a join or link table using just childID, ResponsibleID and relationship (1 or more records per child ID). You'll want a "FamRelationship" lookup table for consistency in your data entry (might be parent, aunt, grandparent, guardian, etc". This way Child Joe can have Parents Mike and Mary, while his cousin child Jane can have Uncle Mike and Aunt Mary. Both Children records would reference the same 2 what you're currently calling "Parents" records.

If a "staff" member is not a member of Board of Directors and it's important to note that, add a tinyint indicator to "staff" (true/false, 1/0).

Martin,

If I am understanding correctly, the employee can be associated with one or more tasks, phases, and projects. This implies a many to many relationship between an employee and a task, phase, or project. If this is the case, throw out the idea of the assignment table completely. Instead, create three different junction tables that can be used to establish the many to many relationships: EmployeeTask, EmployeePhase, and EmployeeProject.

The Task, Phase, and Project tables will allow for relationships to be established as you have defined in your post. The three junction tables will enable an employee to be included in the hierarchy at any of the three levels.

Your SELECT statements will require LEFT OUTER JOINS with the junction tables to pull back the appropriate employee information, which is fine. Adding the junction tables will provide a much more normalized database design.