The rapid integration of inverter-based renewable generation is reshaping power system dynamics by reducing system strength, inertia, and conventional reactive power support, thereby introducing significant stability challenges in weak-grid conditions. While many existing studies rely on single-machine infinite-bus representations, such models do not fully capture the coupled interactions among multiple converters in renewable-rich networks. To address this gap, this paper investigates a Multi-Machine Infinite-Bus (MMIB) system comprising grid-following (GFL) solar and wind farms operating under extremely weak-grid conditions. Such a system captures converter interactions and enables detailed analysis across both weak and strong grid conditions. The study further evaluates the role of a grid-forming STATCOM with energy storage (E STATCOM) as a stabilizing asset capable of actively supporting voltage regulation, damping converter interactions, and improving dynamic resilience. Detailed simulations developed in PSCAD/EMTDC demonstrate that the E STATCOM effectively smooths system dynamics, enhances transient and small-signal stability, and enables stable operation across severe grid-strength variations. The results establish E STATCOM as a scalable and practical solution for strengthening multi-IBR networks and supporting the reliable integration of large-scale renewable generation.