If you want two things to happen "at the same time" you can't put any delay() calls between the two things.
If you want to use delay() to time your blinks AND you want to blink more than one LED at a time you have to:
turn on ALL the LED's you want to blink this cycle.
delay();
turn off ALL the LED's you want to blink this cycle.
delay();
Because of that you can't have separate blink functions for different LED's.