Welcome back and PEACE Raouf,
I will post later a definition of "hypostasis" ( or a link to one) in the classical Greek sense that will help clear this definition bottle-neck.
I can't yet say it's good to be back but we'll see!
I am not sure a definition of hypostasis will help us...I think you need to better define "physis".
The EO confess that Christ is IN two physis and IN two Wills. It seems you link "physis" with "ousia". "Ousia" is that which is common, like the Divine Essence or Human Nature. Ousia does not conotate an individuated instance. So if you say Christ is in two ousia and two wills then He must have the entire human nature and human will within Him. But if Christ's human will is His own human will then it must be hypostatic. If so, then to say Christ is IN two wills must leave room for an interpretation that He is IN two hypostases.
I know that is not what EO say they believe but it is a perfectly logical extension and example of the limitations of language and terminology. As such, I think the expression Christ is OF two natures and OF two wills (without confusion, alteration, separation, etc...) is much better!
It seems the WHOLE point of all our formulas and terminologies is to reject certain heresies...those being Eutychianism and Nestorianism. As long as we keep on insisting on a single formula to the exclusion of all others, we will never get anywhere.
Consider St. Cyril, our common Father, who wrote the following AFTER the formula of reunion:
[Cyril] We say there is one Son, and that He has one nature even when he is
considered as having assumed flesh endowed with a rational soul. As I have
already said, He has made the human element His own. And this is the way,
NOT OTHERWISE, that we must consider that the same one is at once God and
[Questioner] Then he does not have two natures? that of God and that of man?
[Cyril] Well, Godhead is one thing, and manhood is another thing, considered
in the perspective of their intrinsic beings, BUT in the case of Christ they
came together in a mysterious and incomprehensible union without confusion
or change. The manner of this union is entirely beyond conception.
[Questioner] But how from these two things, that is Godhead and manhood, can
we envisage a single Christ?
[Cyril] I think in no other way than as things which come together with each
other in an indivisible union beyond all conception, as I have already said.
[Questioner] Such as what?
[Cyril] Well, do we not say that a human being like ourselves is one, and
has a single nature, even though he is not homogenous but really composed of
two things, I mean soul and body?
[Questioner] We do.
[Cyril] And if someone takes the flesh on its own, separating its unity with
its own soul, and divides what was one into two, have they not destroyed the
proper conception of man?
[Questioner] But if we say that the Son (even considering his as
incarnate)has a single nature surely in is inevitable that we must admit a
confusion and a mixture here, as if he had hidden away a human nature in
Himself. For what would the nature of man be in the face of the pre-eminence
of the Godhead?
[Cyril] My friend, if anyone says that when we speak of the single nature of
God the Word incarnate and made man, we imply that a confusion or mixture
has occurred, then they are talking utter rubbish. No one could convict us
of saying this by the force of proper arguments...
St. Cyril "On the Unity of Christ (SVS Press)
I just don't understand how the EO can consider St. Cyril a great saint and Father of the Church and yet insist that his Christology is heretical and that his terminology ceased to be Orthodox in 451 AD.