Though, how “Orthodox” arethey really? Do they hold to all the tenets encapsulated in the nicene creed? The Athanasian?
The Athanasian creed is a later creed and I don't ever recall reciting that as a declaration of faith but I believe this is due to it length. It can be found in the prayers of early Reformed book of prayers. According to Wikipedia, the Athanasian creed has also been effectively dropped from the Catholic liturgy since the Second Vatican Council. It is however maintained in the Forma Extraordinaria, per the decree Summorum Pontificum, and also in the rite of exorcism. I believe, like the Protestants, it was dropped not over content but of length.
The Westminster Confession has this to say about the Trinity.
Of God, and of the Holy Trinity
I. There is but one only,[1] living, and true God,[2] who is infinite in being and perfection,[3] a most pure spirit,[4] invisible,[5] without body, parts,[6] or passions;[7] immutable,[8] immense,[9] eternal,[10] incomprehensible,[11] almighty,[12] most wise,[13] most holy,[14] most free,[15] most absolute;[16] working all things according to the counsel of His own immutable and most righteous will,[17] for His own glory;[18] most loving,[19] gracious, merciful, long-suffering, abundant in goodness and truth, forgiving iniquity, transgression, and sin;[20] the rewarder of them that diligently seek Him;[21] and withal, most just, and terrible in His judgments,[22] hating all sin,[23] and who will by no means clear the guilty.[24]
II. God has all life,[25] glory,[26] goodness,[27] blessedness,[28] in and of Himself; and is alone in and unto Himself all-sufficient, not standing in need of any creatures which He has made,[29] nor deriving any glory from them,[30] but only manifesting His own glory in, by, unto, and upon them. He is the alone fountain of all being, of whom, through whom, and to whom are all things;[31] and has most sovereign dominion over them, to do by them, for them, or upon them whatsoever Himself pleases.[32] In His sight all things are open and manifest,[33] His knowledge is infinite, infallible, and independent upon the creature,[34] so as nothing is to Him contingent, or uncertain.[35] He is most holy in all His counsels, in all His works, and in all His commands.[36] To Him is due from angels and men, and every other creature, whatsoever worship, service, or obedience He is pleased to require of them.[37]
III. In the unity of the Godhead there be three Persons of one substance, power, and eternity: God the Father, God the Son, and God the Holy Ghost.[38] The Father is of none, neither begotten nor proceeding; the Son is eternally begotten of the Father; [39] the Holy Ghost eternally proceeding from the Father and the Son. [40]