2 Compressor in 1 system

[skhan855]

Hi,
I am making a chiller for injection molding and plan to install 2 compressor in a system being 1 primary and 1 secondary.
Primary would be running at all times while secondary would be used when temperature from primary could not be attained and need extra power for extra load.

I am confused with 2 question and need expert advice.

1) If I install 2 compressors than should I place NRV on both compressors on both suction and discharge side?

2) one of local compressor was advising me to drill a liner horizontal pipe between 2 compressor for compressor oil of both compressors to be equal at all times, according to him if I don't do this then oil on compressor will not be balanced.

Diagram below:
2ndcompressor.jpg

Regards
Salman