Using PID relay to drive multiple contactors
To reduce the risk of EMI pulse noise on contact wire inductance and abrupt current break and nuisance effects on uC, CPU , PC’s etc , I recommend you use ZVS turn on SSR’s and the Triacs have the benefit of zero current turn off.

Then you can gauge the loads within the current rating of the SSR.  Heatsinks may be useful if approaching the limits.

E.g. https://www.omega.com/en-us/control-and-monitoring-devices/relays/solid-state-relays/p/SSRL240-660. 

The closer the sensor is sunk to the heater, the shorter the on/off cycle time. Forced air can also affect this and too close may cause porpoising or motor-boating. With excessive rapid cycles or..not.

Use twisted pair for all wires and shielding for improved EMI reduction.