<p>The increasing deployment of Industrial Wireless Sensor Networks (IWSNs) in smart manufacturing often results in multiple networks operating concurrently in the same area. Without coordination, inter-network interference and inefficient spectrum use can undermine deterministic communication and violate strict reliability and latency requirements. This paper proposes a joint deterministic scheduling scheme for multiple coexisting IWSNs that schedules all networks within a unified time–frequency solution space, enabling concurrent exploitation of time-domain and frequency-domain resources. Specifically, coexistence scheduling is modeled using a multi-dimensional conflict graph (MDCG) that explicitly captures both intra-network and cross-network conflict relationships among candidate link transmissions. Based on the MDCG, the joint scheduling task is formulated as an integer optimization problem and transformed into finding a maximal independent set (MIS) to minimize the overall weighted end-to-end delay across all networks. Since MIS search in MDCGs is NP-hard, we further decompose the global problem into a sequence of hop-level maximum weighted independent set (MWIS) subproblems and develop an iterative hop-wise scheduling algorithm for efficient solving. Extensive simulations under different traffic patterns and coexistence scales show that the proposed method can reduce superframe length and end-to-end delay while improving resource utilization and schedulability compared with representative time-domain and frequency-domain coexistence schedulers.</p>