first i wanna say there are plenty of people who light only 2 candles even if they have kids and i always learned that candles u follow ur mother not ur husband
and to answer the question when pp add candles besides for kids is alot of pp started lighting oil and then the confussion starts so they light two oil then one for each kid then two candles for shomer and zocher which if u ask most rabbenim dont agree to add the 2 candles on top so we can add and add and add