Centrifugal compressors with air intake at different pressures

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There is an existing ethylene refrigeration compressor, as shown in the picture. Ethylene enters at points 1, 2, and 3; the pressure at inlet 2 is equal to the pressure at outlet 1, and the pressure at inlet 3 is equal to the pressure at outlet 2. The mass flow rate at inlet 2 is equal to the sum of the mass flow rate at outlet 1 and the mass flow rate of the fresh air supplied at 2; the mass flow rate at inlet 3 is equal to the sum of the mass flow rate at outlet 2 and the mass flow rate of the fresh air supplied at 3. The question now is: does the mass flow rate of the newly supplied gas from 2 and 3 go directly into the compressors at the 1 and 2 outlets, or do the outlet pipelines of the 1 and 2 compressors mix with the gas supply pipelines from 2 and 3 before entering the compressors? Or do the outlet pipelines of the 1 and 2 compressors lead to a buffer tank, where they mix with the gas supply pipelines from 2 and 3 before entering the compressors at the 1 and 2 outlets?