Origin of Christianity in Kerala

Early Christians/Syrian/St.Thomas Christians

As per historical facts and studies, it is believed that Christianity emerged in Kerala by 52 A.D, after the arrival of St. Thomas in Muziris (Kodungallu, now). He converted several Brahmins and others to Christianity and founded seven churches (Maliankara, Palayur, Kottakkavu, Kokkamangalam, Quilon, Niranam and Nilakkal) in the Malabar coast. 

Some historical proofs that researchers claim for the above are:

Jews who visited Cranganore in 68 AD claims the existence of the Christian community there
Statement of Pantaenus, head of Alexandrian school who visited Kerala in the 2nd century has witnessed the Christian community

//You can see debate all over the internet on this topic. For some, roots from Brahmins thing is a privilege thingy. For some Brahmins, this is kind of less interest topic as they don't want to share their Brahmin pride with other religion! Among Latin and Catholics debate is all about whose roots are from the lower class and whose is from a higher class.
Also, many researchers have rejected this, as proof for this claim is limited//

By 345 AD, the number of Christians further increased, as around 72 families of Syrian immigrants came to Kerala headed by Kanayi Thoma.

Slowly, Christians turned into one of the prominent traders in Kerala and had privileges among the rulers. Socially too, they were treated equally with that of Hindus and played a good role in the social and economic development of Kerala.

Pieces of evidence

Terissappalli copper plate, Tazhakad church inscriptions, that mentions 2 Christian merchants, Copperplate grant issued by Vira Raghava Chakrabarty to a Christian merchant Iravi Kortanan are the primary evidence for the privileges Christian businessmen enjoyed.

This category of Christians followed the Syriac language, rules, and principles. Syriac is considered to be a dialect of Aramaic, the language of Jesus.

Catholic/Latin Christians - Syro Malabar Catholic Church

Latin Christian missionaries who visited Quilon in the medieval period introduced Latin culture of the churches in Kerala. On arrival of Portuguese in the year 1498, this further progressed. St. Francis Xavier and Synod of Diamper (1599) played a big role in Latinisation of the churches in Kerala.

Thus the Christian community in Kerala became 2 factions. Malankara (existing community who followed Church of east/St. Thomas) and Catholics.

Further, this led to incidents such as the Coonan Cross Oath and arrival of Carmelites to convince the existing communities. A section of the existing Christian community was convinced and came under papacy (Rome pope) called as Syro Malabar Catholic Church This, in fact, created friction within the existing community. 

Malankara Syrian Church-Post Portuguese period

Towards the middle of the 17th century, the power of Portuguese declined and Dutch started settling in. This was an opportunity for Malankara church to come out of the Roman Church's control completely and they succeded that with the help of the Dutch.

Break- Up of Malankara Syrian Church - Jacobite

In the year 1910, a section of the Malankara Church wanted to follow Patriarch of Antioch and other faction, Malankara orthodox Church supported local Bishop based out of Kottayam. This break-up was patched up later but again landed in trouble. The dispute on Church was the by-product of this and a verdict was announced by the supreme court of India recently. 

The entry of Church Mission Society (C.M.S) - Anglican Church and Marthoma Syrian Church

By the 19th century, the British entered India and this was an opportunity for C.M.S London to expand its missionary activities to India. In Kerala, they collaborated with Syrian priests which later they would break-up and both started to work their own. The Syrian priests adopted some of the reforms of C.M.S and formed a new Church called Marthoma Syrian Church. Some of the noted reforms include replacement of Syriac by Malayalam as the language of worship. The C.M.S continued their work by forming the Anglican church.

Nestorian/Chaldean church

The Nestorian church is the followers of St.Thomas and is formed from the faction of Church that joined with Romans (Syro-Malabar Catholic church) but wanted more autonomy and freedom from Bishop and thus separated and became independent.

Source of Information:

A Survey of Kerala History- A Sreedhara Menon

Various published news, Church websites, and videos.