Translators should begin a new paragraph here (so Good News Bible, Contemporary English Version).

And when Lysias learned that the king was dead: It is not clear at the beginning of this verse that Lysias was actually bringing up the young prince. We find this information in the final sentence. It is quite legitimate to bring that information forward to the initial position; for example, “Lysias had been bringing up the young son of Antiochus~IV, and when he heard that the king had died.”

He set up Antiochus the king’s son to reign: Philip was with the king when he died, but Lysias, back in the imperial capital, Antioch (1Macc 4.35), had earlier been entrusted with the education of the prince and with the rule of the empire in the king’s absence (1Macc 3.32-33). The king’s dying words thus set up a conflict between his two aides. This clause may be rendered “he made the young Antiochus king in place of his father” (Good News Bible) or “he crowned the boy King Antiochus~V.” Instead of the king’s, the Greek text has “his” (so Revised Standard Version footnote). Revised Standard Version makes the referent clear here. It makes the same type of adjustment in the next clause by rendering “he” in Greek as Lysias.

Lysias had brought him up as a boy: See the suggestion in the discussion above to place this clause at the beginning of the verse.

And he named him Eupator: Eupator (meaning “son of a noble father”) was a throne name, given to Antiochus~V when he assumed power. Apparently Lysias gave the young king this name as a tribute to his father.

An alternative model for this verse is:

• Lysias had been bringing up the young son of Antiochus~IV. And when he heard that the king had died, he made the young Antiochus king in the place of his father, and named him Eupator.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on 1-2 Maccabees. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here.