The language spoke by the Himyarite Arabs is definitely different to the Modern Standard Arabic which resembles the Classical Northern Arabic language.
I remembered when I studied in Folk Religious School (SAR) where my Arabic language teachers said that I was good in Arabic either in the grammar or the pronunciation. I also had a vast vocabulary as compared to other native students, lol. Some of the religious academic teachers including the Arabic ones had tried to stop me from leaving the school just after I clashed with the discipline teacher simply because Sharia stream students were bunch of useless citizens and their classes was beside an unused toilet at the edge of the top level in the school building. Moral of the story, if you wanted your children to have Arabic education, never send them to study in SAR. There was a lack of qualified teachers and I am still following the news about the national "religious and Arabic" education. I believe the situation is still the same. Send your children right away to Arabic speaking schools or simply speak with them in the language at home. Education begins from home.
There were many different dialects spoken by ancient Arabs. The prominent ones in Southern Arabia was the Himyari language and the Sayhadi language. Little is known about the Himyari language and linguists could not find any relation between the Himyari language with Southern Arabic. While being a great kingdom, the knowledge about Himyarite language is very limited and could only be seen through inscriptions written in Sabaean script, which is an Old South Arabian language. The texts written in Himyar language seems to be rhymed. One of them is the Hymn of Qaniya. The language was only known from the statements made by Arab scholars from the first centuries after the rise of Muhammad s.a.w and his teachings. According to their description, the language was not mutual to Arabic speakers. They cannot understand the language at all.
Differently to Old South Arabian languages, which were supplanted by Arabic in 8th century, if not much earlier, the Himyar language continued to be spoken in the highlands of southwestern Yemen after the rise of Islam. According to al-Hamdani (893-947), it was spoken somewhere in the highlands of western Yemen in 10th century, while the tribes at the coast and eastern Yemen spoke Arabic and most tribes in the western highland spoke Arabic dialects with strong Himyari influence. In the following centuries, Himyari was completely supplanted by Classical Arabic. But the modern dialects of the highlands seem to show traces of the Himyari substrate.
The most prominent feature of the Himyari is the definite article am-. It was shared, though with some Arabic dialects in the west of Arabia. Furthermore, the suffixes of the perfect (suffix conjugation) in the first person singular and the second person began with k-, while Arabic has t-.
This feature is also found in Old South Arabian, Ethiosemitic and Modern South Arabian. Both features are also found in some modern Arabic dialects spoken in Yemen, probably through Himyari substrate influence. The article am- is also found in other modern dialects of Arabic in the Arabian peninsula and in Central Africa.
Scholar such as Maryam Bayshak believes that the Shehhi dialect of northern cape of the UAE descends from the Himyari language. Some scholars also claimed that Yemenite Arabic sounds like Assyrian language. And the script of Himyari language is almost similar to the script used to write Ethiopian language, Amharic. Modern Arabic script is the script of North Arabs.
Sealed with prayers for mercy, peace and love, amin!