Hi,
2. Condensers should be piped in parallel with common liquid outlet to receiver - take care about balance lines (you are in Canada and maybe is not bad idea to use louvers to reduce air flow during winter time. Yes in Canada, both screw comp discharge into a common line the flow T's to either condenser. The use louvers is a must here, top and sides.

Receiver would be big enough to collect almost all refrigerant charge. What we can not store in the receiver, we can valve to sales gas compressor and sell. Better than flaring off.

Compressor oil cooling. Glycol circulation is what they want? (Design Engineer)

Production and requirements. Two in unit one and the two screw running full time.

 PLC control you can run all of them, I hope so lol, thats what I am trying to research.

Split suction pressure ... physically separate systems or with back pressure valve? No splitting of lines or BP valves. That is one of my concerns is control. Unit one is run on suction pressure, then we will add Unit two, 200 meter away. (second PT and run off differential pressure?)

Existing system drive motors for compressors. No, unit one has its own condensers and receiver. Yes the two unit receivers will be at different pressures.

15 & -25 deg C, how does that work? We process natural gas so we chill it through kettle style chillers C3 shell and gas tube. The temperature -15 chills the gas to drop out the C3+ hydrocarbons and free water (glycol injection). The colder the temp -25 the more C3+ which improves recovery = money.

Thank you for the info on condensers. We are starting this project next month, but no-one as any info on a control strategy. From what I have researched I can not find an operation in service similar. So I am trying to learn, instead of being fed how it will run.