romuluSnganvaD romuluS puqloD ponglu'
someone calls the romulan "son of romulus"

romuluSnganpu'vaD romuluS puqloDpu' luponglu'
someone calls the romulans "sons of romulus"

Is the above correct ? I can't think any reason it's wrong, but there
is something strange in seeing the {ponglu'} having the {lu-} prefix.

Perhaps it's because I rarely see "someone will call them". I don't know..

When the object of a -lu' verb is third-person plural, you use the lu- prefix. Your sentences are correct.

-- 
SuStel
http://trimboli.name