Scenario: Erev Shabbat, the woman of the house lights the candles, and then the husband and children join on the blessing. Is this permissible? Is this a custom? If it is, what is the source of this custom?
Many "communal" brachot ideas such as this may have originated from the Chavura movement. They where quite popular in the 70's and 80's, and I think they began in the Boston area. As you may surmise by their name, "Chavura" connotes a sense of friendship and communal cooperation in many things including tefilla and ritual. While I can't vouch specifically for candle lighting, I know that for Hamotzi, all the participants would put their hands on the challot and recite the bracha together. Kiddush was also said together, and if I recall, was said on one cup from which everyone drank. Many of the Shabbat rituals were done together, communally.