The word order of the first clause is different in the Hebrew. Literally it says “And the stones shall be according to the names of the sons of Israel, twelve, according to their names.” The focus is on twelve stones, one for each of the names of the sons of Israel. The sons of Israel often refers to all the Israelites. So Good News Translation has “sons of Jacob,” to be more precise.

They shall be like signets is literally “they shall be engravings of a seal.” The same expression is used in verse 11. (See the comment there.) The word like is understood. The meaning is that each stone “is to have engraved on it the name of one of the sons of Jacob” (Good News Translation). For the twelve tribes means “to represent the tribes of Israel” (Good News Translation). This, of course, does not account for the fact that the usual listing of the twelve tribes included Ephraim and Manasseh, the two sons of Joseph, in place of Joseph and Levi. Contemporary English Version has “on each of them the name of one of the twelve tribes of Israel,” omitting the phrase of the sons of Israel. In languages that do not have the passive voice, one may express this verse as “Have them engrave on these twelve stones the name of one of the sons of Jacob [or, one of the tribes of Israel], a different name for each stone.”

Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .