There is no way to call userspace code from an ISR. Unlike system calls which run on the stack of the userspace program, interrupt handlers use internal kernel memory for the stack. Since that memory is not visible in userspace, the system would crash the moment your ISR userspace function finishes or tries to use the stack for local variables (if not before, due to other reasons I have overlooked).

If you need to play with interrupts, you need to write a kernel driver.

There are several things going on in your code. I suspect that what's really causing the problem is that you need to exit the interrupt handler before another interrupt callback can be triggered...but there is also a confusing mix of callback-based handlers and the GPIO.event_detected method.

I think you can simplify things by performing less manipulation of your interrupt configuration. Just have a state variable that starts at 0, increment it to 1 on the first interrupt, so the next time the interrupt method is called you know it's the second interrupt. No need to try setting multiple handlers like that.

Keeping in mind that I don't actually know what you're trying to do...I imagine something like this:

import RPi.GPIO as GPIO
import time

state = 0

GPIO.setmode(GPIO.BCM)
GPIO.setup(26, GPIO.IN, pull_up_down=GPIO.PUD_UP)
GPIO.setup(19, GPIO.IN, pull_up_down=GPIO.PUD_UP)


def interrupt_handler(channel):
    global state

    print("interrupt handler")

    if channel == 19:
        if state == 1:
            state = 0
            print("state reset by event on pin 19")
    elif channel == 26:
        if state == 0:
            state = 1
            print("state set by event on pin 26")


GPIO.add_event_detect(26, GPIO.RISING,
                      callback=interrupt_handler,
                      bouncetime=200)

GPIO.add_event_detect(19, GPIO.RISING,
                      callback=interrupt_handler,
                      bouncetime=200)


while (True):
    time.sleep(0)

You should probably go for an Arduino if performance is really important to you. There are many ways you can get a Raspberry Pi to communicate with an Arduino if you need a Pi to be in your project.

If you have decided on using a Raspberry Pi only, you can use WiringPi if you want to control the GPIO pins with C/C++. You can read the documentation for it here. For more info on programming the GPIO Pins with C/C++, you should read the "Programming with GPIO" section on the Official GPIO Docs. I also found a blog post with instructions on how to go about using C/C++ to work with the GPIO pins.