Grounds for engine switches and solenoids

I'm using a firewall bulkhead connector. Should the grounds for things like the neutral safety switch, reverse light switch, and cam control solenoids be isolated from or tie into the sensor grounds? (which i am crimping together to send through 1 pin) Should they ground directly to the engine, or alternatively I have enough extra pins to take them through the connector and ground at the ecu, which ties into the engine ground point.

Normally you would be using chassis ground, and not the ECU's Sensor Ground (save that for critical ECU sensors). However you have to consider each case and decide if connecting to your engine ground is OK (probably), or it should really go do some other ground (ie, PDM digital input ground if that is where the safety switch input is wired.)