Hi there!
That's not an ideal situation but you should be fine- being able to pick certain things out of a text and do close analysis is a very good skill to have and will get you good marks in the exam!
In terms of the 8 and 10 mark questions- the 10 markers are always linked to a passage they give you and usually entail doing analysis of language and word order and so themes aren't so much of a problem!
For the 8 marker, quite often they involve comparing the two texts, and are usually based around which writer makes their text more exciting/ vivid/ memorable. Or to do with comparisons of characters. Thus I would recommend looking at how each writer makes their text interesting eg. In Cicero the vivid portrayals of characters especially through Sextius' sadistic nature, and also the pathos he creates for the ships captains and the constant reinforcement of this idea!
For Livy I would look at how action packed it is-brief phrases, mayhem and action and also the focus on pietas- the qualities of being a Roman!
Hope this helps a bit and good luck for it!