If the goal is to have all three Bulb Cams’ lights turn on when one of them detects motion, then I think @ssummerlin is correct about using Automations. You’d probably use a Device & Service Trigger so that when one camera “Detects motion” the remaining cameras “Turn on the lights”. I haven’t yet tried this, but I see one potential problem: How do the remaining cameras know when to turn the lights back off? When you set Settings ➜ Bulb Settings ➜ Motion, there’s a Lights Off Timer so that motion-triggered brightness doesn’t remain on indefinitely, but in the Automations Actions for Bulb Cam I’m not seeing an option for something like “Turn on the lights for…{user_defined_time}”. That might be an issue, but—as I said—I haven’t actually tested this.
It might be worth setting up some Automations and trying just to see what happens. Let us know if you need some help with that and/or how it works out.