εγω και ο πατηρ εν εσμεν [John 10:30 TR, undisputed]
I and the Father one are [John 10:30 EGNT ¹]
All three nouns 'I' 'Father' and 'one' are, here, nominative singular, as is the article.
Thus there is no predicate to the sentence and no object complement.
None of the nouns would appear to 'modify' another in any way.
This construction is also noticeable in John's first epistle as well as, here, his gospel account.
ο θεος φως εστιν / God is light [1 John 1:5 / TR, undisputed / KJV]
ο θεος αγαπη εστιν / God is love [I john 4:8 / TR, undisputed / KJV]
James, also, uses the same :
ο θεος εις εστιν / God is one [James 2:19 / TR / KJV]
Would it be correct to say, therefore, that an 'equivalence' is being expressed. The nouns do not modify one another, there is neither predicate nor complement and all that is being stated is that the concepts being expressed by the nouns are, simply but extensively, equivalent, one to the other.
This matter was also introduced in another question two years ago, regarding 'God, consuming fire' : an 'equivalence'.
¹ Englishman's Greek New Testament : Interlinear, Literal, Translation