In the Greek manuscript tradition of Acts 9:25, there are readings found among the manuscripts (these are called variants). The ESV and other modern translations are based on manuscripts that were not availble for the scholars working on the KJV.
Variant 1: "the disciples took him…"
Variant 2: "his disciples took him…"
(Note: labontes = taking, de = but (a postpostive conjunction that comes second in a clause), auton = him, oi mathetai = the disciples, nuktos = night)
The problem is found in the case ending of the third person personal pronoun autos (the dictionary form, translated 'he'). A Greek pronouns as well as nouns has primarily 5 functions that are indicated by case endings (3-5 letter endings attached to the stem of a word; e.g., theou is the genitive/subject form of the Greek noun theos, translated "of God"). The two variants were see in the manuscripts are autou (his) and auton (him). The change in the ending indicates a change in the grammatical function of the word. The former is a possessive use of the pronoun, "his disciples." The latter is uses the pronoun as a the direct object of the verb (labontes de auton), translated "taking him."
I support Variant 2 (the ESV reading). Variant 1 most likely is the result of scribes who thought they were correcting a mistake in the manuscript tradition. The scribe may have believed the reading "the disciples took him" was the original and that it made more sense. But, the majority of scholars and translators (NRSV, NIV, NASB, ASV, RSV) accept the reading "his disciples took him" because it is based on what they consider to be older and more reliable manuscripts. In the practice of Textual Criticism, there is the rule that the more difficult reading is most likely the original text. Explanations are sought after that will explain the existence of variant readings. In Bruce Metzger's A Textual Commentary on the Greek New Testament, he writes
Since it is scarcely conceivable that Jewish converts to Christianity at Damascus would be called "Paul's disciples," various attempts have been made to alleviate the difficulty which the best attested reading involves. Occasionally the genitive autou is construed as the object of labontes ("taking hold of him"), but the sequence of words as well as the unnatural sense stand against this expedient. To assume… that these disciples had been Paul's "companions on the way to Damascus, who through his own leadership and by his witness had themselves come to the faith," is totally gratuitous. The most satisfactory solution appears to be the conjecture that the oldest extant text arose through scribal inadvertence, when an original auton was taken as autou. (page 366)
Although "his disciples" is a strange reading, we must understand that Acts was most likely composed over time and pieced together by Luke. The textual history of Acts is interesting. When reading Acts you may have notice that sometimes the narrator will shift from third-person narration to speak in the first person "we/us" (e.g., Acts 16:16). I think this shift demonstrates that Luke wrote the various sections of Acts at different times, places, and circumstances.
It's important to know what the history of the biblical text because the New Testament is determine from about 5,000 manuscripts (most in Greek but in other languages as well such as Coptic, Ethopic), because we no longer have the original manuscripts of the New Testament. The NT was copied by scribes over 1,500 years until the invention of the printing press.The text of the Hebrew Bible is a different story (e.g., The Masoretic Text and the Dead Sea Scroll). It was professionally and meticously copied because it was regarded as Scripture. The NT documents were initially not regarded as scripture, because Paul and the other NT writers wrote letters. The Gospels and Revelation have their own unique textual history. Today, scholars construct "critical text/editions" of Bible that are the result of evaluating and comparing the many manuscripts. Each manuscript is compared with those that are like and unlike it. They have been placed in textual families based on similar traits that seem to connect them back to early parent texts. Each NT book has its own textual history. The NT was not a collection of books from the beginning. The canonization of the Bible happened later. Textual Criticism is the science/art of determining the original word of the biblical text. Before translation and interpretation of the Scriptures, we must determine the wording of the Hebrew, Aramaic, and Greek texts of the Bible. Remember manuscripts were hand copied, so scribe errors were inevitable (aural mistakes, omissions, dittography, haplography, homoioteleuton, homoioarchton, scribal corrections). There are major and minor variants between these many copies must be evaluated. The best reading is selected based on principles that I'll outline briefly below. Please note that no major biblical doctrine about God, the Lord Jesus, sin, salvation, and so on are compromised by these textual variants. The textual history of the Bible is important but we have great confidence in our Bible even where there is a discrepancy between manuscripts.
The Twelve Basic Rules for Textual Criticism (Source: The Text of the New Testament an Introduction to the Critical Editions and to the Theory and Practice of Modern Textual Criticism by Kurt Aland and Barbara Aland)
The translator has the difficult task of deciding which variant is the original reading of the text. This is not an easy task. It is so important to do research and to enter into a conversation with those who have wrestled with the same challenges.
Here are some books and resources that will help: