You need proof that the skills of both physicians were necessary. Since pneumonia and sepsis are both infections that can be cared for by hospitalists, why do you need the skills of 2 physicians. Are the doctors both employed by the same entity (hospital)? If so, you can bill just one visit per day - regardless of who treated which dx.
As a former Medicare Part B employee (coder, appeals, hearings, etc.), I can tell you that they will not pay more than one physician to deal with a problem or series of problems that are within the scope of practice of one physician. It's not as simple as each physician having a different dx. You've got to justify the need for both.
Progress notes showing who did what, why the other physician wasn't available, that the sepsis was outside the skillset of the first physician or that the physicians were of different specialties. Was the first physician in primary care and the second physician a specialist in infectious disease? If so, they would expect to see the infectious disease doctor take over the case and manage it without the involvement of the primary care doctor.
Look at progress notes and order sheets. But don't expect them to pay for both. We didn't.