code:

int candle_states[12] = {0,0,0,0,0,0,0,0,0,0,0,0};
int button_pins[12] = {1,2,3,4,5,6,7,8,9,10,11,12};
int led_pins[12] = {13,14,15,16,17,18,19,20,21,22,23,24}; 
bool button_state[12] = {false, false, false, false,false, false, false, false,false, false, false, false};
bool last_button_state[12] = {false, false, false, false,false, false, false, false,false, false, false, false};

//setup all your pins and stuff here

void loop () {
for (int i = 0; i < 12; i++) {  //loop and check all buttons in sequence
button_state[i] = (digitalRead(button_pins[i]) == LOW) ? true : false;
  if (button_state[i] && !last_button_state[i]) {  //if the button in question was just pressed
    candle_states[i] = !candle_states[i];  //invert this button's candle
    candle_states[ (i+1)%12 ] = !candle_states[ (i+1)%12 ];   //invert the next one in sequence, wrapping around to 0 if we're at index 11
    candle_states[ ((i-1)+12)%12 ] = !candle_states[ ((i-1)+12)%12 ];  //invert the previous one in sequence, also wrapping around backwards
    last_button_state[i] = button_state[i];
  }
}

for (int i = 0; i < 12; i++) {
  digitalWrite(led_pins[i], candle_states[i]);
}

}