The atmospheric characterisation of multiple exoplanets in the same system can provide a window into the processes that underpinned their formation and evolution. The planetary C/O ratios are of particular interest as they encode information about where the planet formed with respect to different ice lines, but precise measurements of this using current instrumentation have proved challenging. Recent observations have revealed that the nearby late K-type star TOI-178 hosts a compact system of at least six transiting exoplanets with R < 3 Earth radii, five of which form a chain of Laplacian resonances. Alongside the fact that the large planet-to-planet density variations present in the system appear difficult to theoretically explain, its resonant chain and large atmospheric signal sizes provide a well-constrained laboratory to test the main formation theories. We propose to use JWST/NIRSpec in BOTS mode with the G395M grating to observe single transits of TOI-178 b, d, and g, providing an atmospheric characterisation of planets that span the full range of known orbital separations from the host. Amongst other things, our mock retrievals suggest that the strong constraints that we will be able to place on the abundances of H2O, CO, CO2, and CH4 will enable a precise derivation of the C/O for each planet. The combination of these measurements will facilitate the first detailed observational study using the C/O to test whether multiple planets in the same system formed in situ or migrated to their current positions.