Thousands of candles can be lighted from a single candle, and the life of the candle will not be shortened\. Happiness never decreases by being shared\.
Well. Actually.
Lighting other candles from the first, as well as if they're burning nearby, would have various effects on the first candle. The increased heat would make the first candle's wax evaporate more, and thus burn brighter as well as decreasing its lifespan.
If there's not enough ventilation in the room, the addition of other fires would reduce the available oxygen, and thus reduce the burning intensity and increase the lifespan of the initial candle, as well as make the flame more yellow than blue.
If there's no ventilation at all, lighting too many candles will make them all burn out prematurely.
End. Well. Actually.