Yes. The Father and the Son are one principle of the Holy Ghost because there is no relative opposition between them as the principle of the Holy Ghost.
The Father and the Son are in everything one, wherever there is no distinction between them of opposite relation.
Although this word "principle" signifies a property, it does so after the manner of a substantive, as do the words "father" and "son" even in things created. Hence it takes its number from the form it signifies, like other substantives. Therefore, as the Father and the Son are one God, by reason of the unity of the form that is signified by this word "God"; so they are one principle of the Holy Ghost by reason of the unity of the property that is signified in this word "principle."
If we consider the spirative power, the Holy Ghost proceeds from the Father and the Son as they are one in the spirative power, which in a certain way signifies the nature with the property. Nor is there any reason against one property being in two "supposita" that possess one common nature. But if we consider the "supposita" of the spiration, then we may say that the Holy Ghost proceeds from the Father and the Son, as distinct; for He proceeds from them as the unitive love of both.