...quem gens Iulia auctorem...

Latin Learning Latin
1

I’m trying to understand the below. It’s Orberg’s adapted Livy from LLPSI Cap. XLI.

Nondum maturus imperio Ascanius, Aeneae filius, erat; tamen id imperium ei ad puberem aetatem incolume mansit. Interim Lavinia pro puero regnavit. (Incertum est - quis enim rem tam veterem pro certo [= certo (adv.)] affirmet? - hicine fuerit Laviniae filius an filius ille maior, Creusa matre natus, Ascanius sive Iulus appellatus, quem gens Iulia auctorem nominis sui esse dicit.)

I don’t usually translate but I want to be sure I’ve got this right:

Not yet ready to be emperor Ascaius was Aeneas’ son; despite the purple having been reserved for him since the time of his youth [ad puberem aetatem]. During that time Lavinia reigned on his behalf. (It’s not certain - who could confirm such an ancient thing - whether he was the son of Lavinia or the older brother, son of Creusa, Ascanius, also called Iulus, [and here’s where I am unsure] who the Iulian tribe say is the beginning of its name…

What I’m really not sure about is the construction (subject - object relationship) of this last part. ‘Ascanius sive…dicit’

2

You basically got the last part right. Just beware of the demonstrative ille, as I understand it, it prepares the arrival of the last proposition :
« …wether he was Lavinia’s son or this eldest son (born of Creusa, called Ascanius or Iulus), whom the Julian family considers to be the origin of their name.»

Your translation of the first two sentences is wrong.
Nondum maturus imperio Ascanius, Aeneae filius, erat ;
Ascanius, (Aeneas’ son), was not yet ready for power ;

tamen id imperium ei ad puberem aetatem incolume mansit.
Nevertheless, this power remained intact for him until his puberty.

3

Many thanks Shenoute