Are WLC's arguments against Relative Identity Trinitarianism valid?

In his book *Philosophical Foundations for a Christian Worldview*, William Lane Craig offers three arguments against Relative Identity. The first argument regards the alleged "spurious" nature of relative identity. Craig, quoting Peter Van Inwagen, argues that there are no known cases of relative identities that cannot be analyzed in terms of classical identity > Peter van Inwagen has sought to defend the coherence of such creedal > affirmations by appeal to relative identity. According to this notion, > the identity relation is not absolute but is relative to a sort of > thing. For example, we say, “The couch is the same color as the chair” > (not “The couch is the chair”) or “The Lord Mayor John is the same > person as the schoolboy Johnny” (not “The Lord Mayor is the schoolboy > Johnny”)... The fundamental problem with the appeal to relative > identity, however, is that the very notion of relative identity is > widely recognized to be spurious. Van Inwagen himself admits that > apart from trinitarian theology, there are no known cases of allegedly > relative identities that cannot be analyzed in terms of classical > identity. Our example of the couch and the chair is not any kind of > identity statement at all, for neither piece of furniture literally is > a color; rather, they have the same color as a property. The example > of the Lord Mayor is solved by taking seriously the tense of the > sentence; we should say, “The Lord Mayor was the schoolboy Johnny. The second argument is that if x and y can be the same N but not the same P in a relative identity statement, they also can't be the same anything. > Suppose that two things x and y could be the same N but could not be > the same P. In such a case x could not fail to be the same P as x > itself, but y could. Therefore, x and y are discernible and so cannot > be the same thing. But then it follows that they cannot be the same N, > since they cannot be the same anything. Identity must therefore be > absolute. Craig's third argument is that it is doubtful that x and y can be the same being without being the same person. > [E]ven granted relative identity, its application to trinitarian > doctrine involves highly dubious assumptions. For example, it must be > presupposed that x and y can be the identical being without being the > identical person. Notice how different this is from saying that x and > y are parts of the same being but are different persons. The latter > statement is like the affirmation that x and y are parts of the same > body but are different hands; the former is like the affirmation that > x and y are the identical body but are different hands. Van Inwagen > confesses that he has no answer to the questions of how x and y can be > the same being without being the same person or, more generally, how x > and y can be the same N without being the same P. It seems, then, that > the ability to state coherently the trinitarian claims under > discussion using the device of relative identity is a hollow victory. Are these valid critiques of Relative Identity Trinitarianism?