This Paper Proposes a Decentralized and Coordinated Voltage and Frequency (V-F) Control Framework for Islanded Microgrids, with Full Consideration of the Limited Capacity of Distributed Energy Resources (DERs) and V-F Dependent Load. First, the Concept of DER Inadequacy is Illustrated with the Challenges It Poses. Then, a Decentralized and Coordinated Control Framework is Proposed to Regulate the Output of Inverter-Based Generations and Reallocate Limited DER Capacity for V-F Control. the Control Framework is Composed of a Power Regulator and a V-F Regulator, Which Generates the Supplementary Signals for the Primary Controller. the Power Regulator Regulates the Output of Grid-Forming Inverters According to the Real-Time Capacity Constraints of DERs, While the V-F Regulator Improves the V-F Deviation by Leveraging the Load Sensitivity to V-F. Next, the Static Feasibility and Small Signal Stability of the Proposed Method Are Rigorously Proven through Mathematical Formulation and Eigenvalue Analysis. Finally, a MATLAB-Simulink Simulation Demonstrates the Functionalities of the Control Framework. a Few Goals Are Fulfilled within the Decentralized and Coordinated Framework, Such as Making the Best Use of Limited DERs' Capacity, Enhancing the DC Side Stability of Inverter-Based Generations, and Reducing Involuntary Load Shedding.