Seems like you need a relationship between employees and the table of dates available rather than the table of skills.
Employees::__pk_EmployeeID = Skills::_fk_EmployeeID
Employees::__pk_EmployeeID = DaysAvailable::EmployeeID
MasterSchedule::Date = DaysVailable::Date
A Portal to skills placed on the MasterSchedule layout should list all skills from all employees that are available on that date.