Could Jesus have extraterrestrial brothers or sisters? According to Sacre Scriptures, Gospel, Catechesis, Catechism and so on, could Jesus have had, or could have, one or more brothers or sisters?

I'm not referring to terrestrial brothers or sisters who lived during the time Jesus has lived on the earth, which, however, would be in disagreement with the dogma of the Virgin Mary(1),  but to brothers or sisters  that lived on other planets where other kinds of extraterrestrial beings live or lived.

Or, in case, did God send always Jesus, the same son who went on the earth, on these planets?

I'm not looking for an opinion based answer, but for an answer that describes the position of diffrent christian churchs on this matter(2).

(1) However, there would be the problem to exclude the circumstance that Joseph, the 'father' of Jesus, did not have other son/s with other women.

(2) If it is unclear, the matter is what the position of christian churches is about extraterrestrial civilizations and their need to be saved.
Firstly, anything and everything regarding "other planets" is speculation. The Bible is entirely silent on the matter. That includes the question of whether or not there is intelligent life on other planets. Scientists disagree on that question, as do theologians; most theologians, I gather, would say that there probably is not. But let's assume for the sake of your question that there is.

We can say unequivocally based on Scripture that the answer is no. Jesus is "God's only begotten son," as he proclaims in the ever-famous John 3:16. The Nicene Creed summarizes Scripture's teaching this way:


  I believe in ... 
  one Lord Jesus Christ, the only-begotten Son of God,
  Begotten of his Father before all worlds,
  God of God, Light of Light,
  Very God of very God,
  Begotten, not made,
  Being of one substance with the Father,
  By whom all things were made;


This is very important. Colossians 1:15-20 is a good passage about Christ as the agent of creation. That's a unique role, which he shares with no one. He was not created, nor was he begotten in a moment in time. The trinitarian relationship of Father, Son, and Holy Spirit has existed "before all worlds," and is unchangeable. 

This being so, you may ask, how would redemption be accomplished for other intelligent life that has gone astray?

That's a question none but God knows the answer to. Nor does any church I'm aware of have an "official stance" on the matter. But some answers will be consistent (as far as they can go) with official teachings, and others won't. A good piece of speculation can be found in C. S. Lewis' Religion and Rocketry:


  Perhaps of all races we only fell. Perhaps Man is the only lost sheep; the one, therefore, whom the Shepherd came to seek.


Lewis raises this as a possibility, but affirms that it is not the only one:


  [But] if we knew that Redemption by an Incarnation and Passion had been denied to creatures in need of it is it certain that this is the only mode of Redemption that is possible? ... [W]e don't know. At any rate, I don't know. Spiritual as well as physical conditions might differ widely in different worlds. There might be different sorts and different degrees of fallenness. We must surely believe that the divine charity is as fertile in resource as it is measureless in condescension. To different diseases, or even to different patients sick with the same disease, the great Physician may have applied different remedies.


In the essay itself, he doesn't go very much further with regard to what these "different diseases" and "different treatments" may be. But an imaginative rendering of his speculation is found in his brilliant Space Trilogy, which I highly recommend. The only concrete piece of further speculation he offers in the essay is that perhaps other species' redemption would come about via Christ's sacrifice on earth. But this, again, is mere speculation.

So that answers (as well as I can) about redemption. What about other species not in need of redemption? Surely they would still need to at least know God. So, would Jesus necessarily visit other planets in order to reveal God to them? Perhaps. Again, speculation. But what we do know is that if these were species that God desired to love as his children, he would not leave them without the Holy Spirit, who Jesus tells us is our comforter and who indwells us for our holiness and renewal.