I am not sure whether you mean that these words are uttered by Pilate or a narrator.
Let us build the sentences in both cases.
Whichever you intended, I hope the differences are illuminating.
I will not touch your vocabulary apart from one word:
efferre is "to carry out" in a concrete way, not in the idiomatic English sense of completing a task.
I will use gerere instead.
(Also note that reddere > redditurus but redire > rediturus.)
Whether the words I chose are perfect is less relevant; my focus here is on syntax.
Direct speech
Let us first work with direct speech, where your sentence is a direct quote from Pilate.
The full sentence in English would then be:
Pilate said: "He, Caesar, is not about to return a position to you, to which you are not suited, that you are not able to do."
The only difference to yours is that I added some punctuation.
If the "he" refers to someone other than Caesar, please clarify the English sentence.
Now Pilate is saying directly what Caesar will do, and no indirect speech is involved.
The first part would be:
Caesar ille non tibi reddet officium.
That Caesar will not give back to you the position.
In both languages it would be more natural to put officium/"position" earlier, but I want to refer to that word by relative clauses, so I put it to the end for clarity of reference.
The position is described by two relative clauses which are simply listed one after the other.
This strikes me as a little unusual, but not wrong, especially in spontaneous speech.
It helps me parse it if I supply an "and".
If the relative clauses are coldly factual — Pilate agrees with Caesar that the colleague is inept — then they can be rendered with the present indicative.
In this case they just describe how the world is:
Caesar ille non tibi reddet officium, cui non es idoneus et quod non potes gerere.
That Caesar will not give back to you the position, to which you are [really] not suitable and which you [really] cannot execute.
If the relative clauses are not facts but Caesar's opinions — from Pilate's point of view — then a conjunctive is in order:
Caesar ille non tibi reddet officium, cui non sis idoneus et quod non possis gerere.
That Caesar will not give back to you the position, to which [he thinks] you are not suitable and which [he thinks] you cannot execute.
Indirect speech
Suppose there is a narrator telling what Pilate said.
The full sentence in English would then be:
Pilate told him that Caesar is not about to return a position to him, to which he is not suited, that he is not able to do.
Notice that a lot of the pronouns are different.
The narrator speaks to the audience, not to Pilate or his colleague.
What used to be "you" is now "he".
The very beginning is still direct:
Pilatus ei dixit.
Pilate told him.
Then comes what Pilate told, and this is given through indirect speech using an accusativus cum infinitivo:
Pilatus ei dixit Caesarem ei non redditurum esse officium.
Pilate told him that Caesar was not going to return to him the office.
The colleague should be ei.
The reflexive sibi would refer to the subject of either the dominant or the subordinate structure (Pilate or Caesar).
Now the reasoning is now best considered subjective, be it Caesar's or Pilate's opinion.
Therefore I would render the relative clause in subjunctive.
Pilatus ei dixit Caesarem ei non redditurum esse officium, cui non sit idoneus et quod non possit gerere.
Pilate told him that Caesar was not going to return to him the office, to whichhe is not suitable and which he cannot execute.
The relative clauses are subordinate to a future participle redditurum and thus take the present tense.
The answer to the question about subordination to ACI says that the relevant tense is that of the ACI, not of the structure governing it.
It is not immediately clear who the subject of the relative clauses is.
It could be Pilate, Caesar, or the colleague, and I cannot see a pronoun that would disambiguate well here.
But in context it is clear enough.
