Can be replacing Raspberry Pi 4 by Raspberry pi zero and The Pixhawk Autopilot by mini Pixhawk PX4 Flight Controller or not because I need put it in the small space
Hi @AMR, welcome to the forum 
This isn’t a configuration we’ve tried, so I can’t provide guarantees on whether it would work well.
Others on the forum have seemingly used the Pixhawk 4 mini (or at least tried to do so), and I expect ArduSub should run on it. From a quick look it doesn’t seem to have obvious missing features that would be required to operate an ROV.
BlueOS should be installable on a Raspberry Pi Zero, but it may be challenging to set up appropriate powering and connections, and it may not have enough processing power to run at full capacity. The newer Raspberry Pi Zero 2W uses a similar main processing chip to the Raspberry Pi 3B, so has a better chance of working ok, but may still be difficult to set up properly.
It’s an interesting use-case, so please do let us know if you try it successfully
If you try it and run into problems we can try to provide some advice on what may be required to fix it / get it working, but right now it’s not a priority for us to do that testing and verification ourselves.
Daer Eliot
Can be replacing Raspberry Pi 4 by Raspberry pi zero 2W only
T&R
AMR
As above,