What is parent process of all the processes in iOS?
The name of the equivalent process on iOS and macOS is launchd.

It is run with PID 1 and it the parent of all other running user-space processes. The objective of launchd is similar to initd - having the responsibility of launching other processes during boot and various other phases of the system lifetime.

This is in thread with traditional Unix-based systems, where PID 1 is reserved for the process that is responsible for launching the user space part of the system. This was traditionally initd, but on modern systems that is often replaced with alternatives such as launchd (on macOS), systemd, upstart, and other init systems.