there's hundreds of sw engineers working on driver software for both windows and linux. i gather the "two guys" thing is a bit of a gag but like, there's dozens on kernel mode driver development alone. there's each individual team for usermode drivers (d3d9 and below, d3d10 and 11, d3d12, opengl, vulkan). there's display abstraction layer, there's firmware and security, multimedia and video, gfx compute (opencl, hip+rocm, others), user interface, packaging and install, audio, and many more i'm surely missing.
if two people could cover those domains in their entirety, i would seriously be impressed.