Trying to understand how to make this door mechanism work

I'm trying to wrap my head around how redstone works but i'm kinda struggling with some stuff. I can sometimes get this door to open on one side or the other depending on where i put the repeater but never both because one side gets left behind(like in the 3rd picture), or if i can get both to move the pistons at the back don't push forward. I've tried moving around repeaters every different way and with different delays but it doesn't seem to work. Maybe I'm doing something wrong. I replaced the pressure plates that i want this to be powered by just so i can see the redstone in its active state without it turning off.