To spare others, being part of a household doesn't extend the lifetime of all household members, only extends those that had activity.
This Is part of a response from BA .
To keep your Avios active you need to collect, spend, purchase or transfer Avios at least once every three years. In fact, it is one of the conditions of membership that if you have no eligible activity on your account for a period of three years your Avios are removed. If you are in a Household Account these conditions apply to each individual Member.