May the guilt of their blood reston the head of Joab and his descendants forever.
But on David and his descendants, his house and his throne,may there be the LORD's peace forever.
This structure is also in the Hebrew:
וְשָׁבוּ דְמֵיהֶם
בְּרֹאשׁ יוֹאָב וּבְרֹאשׁ זַרְעוֹ לְעֹלָם
וּלְדָוִד וּלְזַרְעוֹ וּלְבֵיתוֹ וּלְכִסְאוֹיִהְיֶה שָׁלוֹם עַד־עוֹלָם מֵעִם יְהוָֽה׃
And the Latin Vulgate:
et revertetur sanguis illorumin caput Ioab et in caput seminis eius in sempiternum
David autem et semini eius et domui et throno illiussit pax usque in aeternum a Domino