Job A starts job B, C, D and E. Additionally, the jobs C and D are starting each other more jobs e.g. C1, C2, D1 and D2. The joined job F should start when all ends (in this scenario: B, C1, C2, D1, D2 and E) are finished.

Maybe this can be achieved by a text box in which the jobs which needs to finish first can be entered if the multiple downstream levels isn't supporting this.