My niece's baptism is next week in a greek orthodox church, ideally I don't want to go but this will no doubt start a fight with my wife, I'm thinking of just sitting in the back away from my wife and kids although this too will upset her, I believe the Catholic teaching on this is I should not attend, wondering what some here would do in my situation.

Well, it's a valid baptism.

I think the Catholic teaching is that you attend where not attending would cause a rift in the family.

I don't have sources, that's what I've heard.  It sounds like if not going is going to cause turmoil, you should go.

Besides, the infant is being cleansed of original sin and being made a Catholic until she is old enough to reject the faith on her own.  Hopefully there will be enough Catholic influence in her life to get her going in the right direction.

what do you make of the following?


Pope Pius XI,
Mortalium Animos
(# 10), Jan. 6, 1928: “...
this
Apostolic See has never allowed its
subjects to take part in
the assemblies of non-Catholics
...”
2
All Catholic moral theology manuals before Vatican II
reiterated this truth.
They taught that it’s
a mortal sin against the divine law for Catholics to partake in non-Catholic worship.
Pope Pius IX,
Neminem vestrum
(# 5), Feb. 2, 1854: “We want you to know that those same
monks sent Us a splendid profession
of Catholic faith and doctrine...
They eloquently
acknowledged and freely received the regulations and decrees which the popes and
the sacred congregations published
or would publish – especially those which
prohibit
communicatio in divinis
(communion in holy matters) with schismatics
...
They acknowledge that they condemn the error of the schismatic Armenians and
recognize that they are outside of the Church of Jesus Christ.”

Notice that the decrees and regulations of the
popes prohibit communication in divine things
with schismatics.
Pope Pius VI,
Charitas
(# 31-32), April 13, 1791, speaking of priests who went along with
the notoriously heretical civil constitution of
the clergy in France: “Above all, avoid and
condemn the sacrilegious intruders...
do not hold communion with them especially in
divine worship
.”
4
Speaking of priests who belong to the “Old Catholic” sect, which publicly rejects Vatican I and its
definition on Papal Infallibility, Pope Pius IX declared:
Pope Pius IX,
Graves ac diuturnae
(# 4), March 23, 1875: “
They [the faithful] should
totally shun their religious celebrations, their buildings,
and their chairs of pestilence
which they have with impunity established
to transmit the sacred teachings. They
should shun their writings and all contact with
them. They should not have any dealings
or meetings with usurping priests and apostates from the faith who dare to exercise the
duties of an ecclesiastical
minister without possessing a legitimate mission or any
jurisdiction.”
5
Canon 1258.1, 1917 Code of Canon Law: “It is
not licit for the faithful by any manner to
assist actively or to have a part in the sacred rites of non-Catholics.”

You are Aunt and Uncle.  You do not have to be there.  You are the dad, you make the decision whether wife likes it or not.  If it is not catholic, don't go.  I wish my husband would have stood up and taken charge when we were younger.  The children need to look up to dad and if they see a false peace, it teaches them nothing.  So, if you as dad and husband decide not to go, you must say why.  Greek orthodox are in schism. It cut itself off from the parent tree of catholicism.  It denies the Catholic dogma that the Holy Ghost proceeds from the Father and the Son.  It also teaches that the souls of the just will not attain complete happiness till the end of the world, when they will be joined to their bodies; and that the souls of the wicked will not suffer complete torture in hell until that last day.  These are heresies against the doctrines of Holy Mother Church.

If you go, who could give the impression that you are indifferent to religions and it is ok.  This is the perfect opportunity to be head of the family.  St. Joseph pray for us.