according to the followers the Eastern orthodox churches is the true church?

I am Roman Catholic and I believe the true church is in the orthodox churches that follow the bishop of Estambul and the Roman Catholic because they have the right apostolic secession and the sacraments are valid no? both churches have many things in common.

A pointless debate. All churches and religions are simply hocks-pocus created by humans.

There are several churches that follow the Apostolic Succession - the Orthodox, Roman Catholic, Anglican, Lutheran (at least one branch, but I think all), and others.

Think of an apple. Cut it into two - which half is the "real" apple? The church is like that - both RC, and the Orthodox can claim, with some justification, to being the "real" church, as can Anglicans, and others. They are all correct, despite being different.

Read Paul's writings to the various churches he founded. Even in his time there were differences, but still in the same church.

Catholics and Orthodox have more differences than similarities

here are some if them

Catholics changes the Doctrine, Peotestants changed it even more, no one can claim apostolic succession except Catholics and Orthodox

http://www.ocf.org/OrthodoxPage/reading/ortho_cath.html

Accortdong to the EO Christian the Church funded on Pentecost is the EO Church. We follow not a bishop of Instanbul but Jesus Christ.

The Eastern Orthodox Church uses the title "Holy Orthodox Catholic and Apostolic Church", and has the same early history as the Roman Catholic Church, and a known and recognized apostolic succession. There were five ancient patriarchates -- Rome, Constantinople, Alexandria, Antioch, and Jerusalem. Even though Rome departed their company, the remaining four are still today the major Christian Centers in the East, in influence, if no longer in population.

The Ecumenical Patriarch of Constantinople (now Istanbul, Turkey) is the chief bishop in honor in the Eastern Orthodox Church, but is not the head bishop of all Orthodox Christians, by any means. There are more Christians with the Patriarch of Moscow as their chief bishop than any other, for instance.

first the Bishop in the city of Istanbul is the Patriarch of Constantinople- the name Istanbul is not that popular is it reminds the Greeks that they lost the entire Eastern Roman Empire to the Muslims.
Second- the Copts Armenians and Syriacs who have Pope Shenuda as their lead patriarch would have issues with this question as they would wonder why you believe the Eastern Orthodox have valid apostolic secession but not the Oriental Orthodox. On the basis of what it means to have Primacy they are closer to us in the Eastern Orthodox church than you Catholics.
Primacy is a position of Honor and not authority for you in the west you have doctrines like- papal infallibility which from my understanding means that in issue of despite the Pope has the final word.
Where for us Eastern Orthodox the only role the Patriarch of Constantinople plays- is he can call a general council. Next we have issues like how we understand the Original sin-a late medieval -Renaissance council held by the RC claimed that our Orthodox view of the original sin- and how we don't inherit guilt just that mentioned in the book of Genesis to be heresy. We also find your teaching on purgatory and indulgences to be heretical then there the issues of the pique.