Dear,
You know Shiro does not get along well with your other cats, why is he left out at night? To be safe, you should cage him whenever you are not able to supervise on him.
He and his other sibling and even half sibling has that same connection of peeing and pooing whenever Really-Really scared... Infact most cats will do that, so you can't blame him for that...
If you rally feel hard, I have offered you to take him as I know and trust a good friend of mine who is able to care for him...
Do consider it again cuz you really can't seem to handle him like this...
Shiro is a male, so is my Oren...
All their siblings have pretty faces which confuses people about their gender...
Most male cats will have that "jantan" look... But them, they have the "jambu" look

Yes, most cats will poo and pee if they are Really-Really scared.
Do consider my offer again.
I'm just wishing for the well being of Shiro.

KP
i did everything for him..fyi,i did cage him at night.
he peed and pood in his cage! in case u missed it,the cage has the bars,rite..