@Megahertz, not this design is technically not good enough. It might work under much specified conditions but it's just not the right way. You don't have to power up 4 slaves from one microcontroller. Instead, just power them up from the regular supply and give an option to the master controller to halt or reset them at any time. This not only gives you extra options for your design but also removes the vulnerability. Also, you can't provide one input to multiple controllers, it might lead to voltage dropping which will make the signal disappear, instead use simple buffers in between to ensure the signal reaches all the required pins. Hope that's helpful.