In SCA usage, Squires, Apprentices and Proteges are sometimes collectively referred to as dependents. This is probably to avoid using the term vassal since not all relationships between a Peer and his/her dependents involves fealty.
With the creation of the Order of Defence the situation becomes more complicated. With various Kingdoms already having established fencing traditions it seems unlikely that there will be an SCA-wide term for the dependents of Masters of Defence. For example, the East Kingdom appears to be settling on provost, while in Drachenwald that term is already in use by the Academy of Defence.
See also S.A.P