I operated both my daughters then BAEC accounts through a single email address as me for many years when they were minors. By default the BA IT will reject using a single email but a human being at BA can override this so a phone call in required to set it up.
Do they reject the email+ route? That is, a gmail account you already have with “+name” added. So cwl@gmail dot com, and add them as cwl+favorite@gmail dot com and cwl+lessfavored@gmail dot com…and all the emails go to the base gmail account.