How to maximise socioeconomic activities while retaining the effect of COVID-19 endemic under control is an essential topic when many countries have decided to live with COVID. In this paper, we show how optimal control can be used to classify the importance of non-pharmaceutical interventions (NPIs) to counter an epidemic under different expectations. We focus on the modelling of small environments, such as schools, universities, and care homes, where the population can be separated into two distinctive subgroups. We propose a model for such a scenario, we compute the associated basic reproduction number and we provide conditions for stability. Finally, we formulate an optimal control problem and, by means of simulations, we show that the relative importance of the interventions naturally emerges from the optimal policy.