two Service Appointments assigned to two different resources is the appropriate Field Service design.
Because the technicians can arrive at different times, their work must be independently schedulable. Separate Service Appointments allow each technician to have independent timing, travel, and assignment while still supporting the same overall job.
Salesforce Field Service treats the Service Appointment as the primary unit of scheduling. Scheduling Policies combine Work Rules, which determine whether a resource or time slot is valid, with Service Objectives, which score valid alternatives against business priorities. The selected configuration therefore has to operate at the scheduling layer rather than merely changing descriptive fields on the parent Work Order.
The alternatives address different parts of the Field Service model. A single appointment with two resources is more appropriate for a crew-style simultaneous visit, and Required Resources on one appointment would not provide separate scheduling windows.
This approach keeps the implementation aligned with the standard Field Service data model and avoids unnecessary customization. Study Guide reference: Managing Scheduling and Optimization - Multiple Service Appointments; independent resource scheduling.