in scaphas conscendere = to board the small craft
quam celerrime = as fast as possible
cuperent = they wished

Let's take it all from the beginning now :
Consulatum inierunt Pompeius et Sulla qui bello contra Pyrrhum inter clarissimos duces fuerat. Sulla diu ita se gessit ut nullum consilium petendi
consulatum habere videretur. Eum honorem undequinquagesimo anno
aetatis accepit.
Pompeius et Sulla acceded to the consulate (they became consuls) ; Sulla
(= qui) had been amongst the most famous generals [to take part] in the war against Pyrrhus. He (= Sulla) behaved for a long time in such a way that he
seemed to have no intention whatever to aim at the consulate (= he behaved as if he was not interested at all in becoming a consul). He received this
magistrature/public office (= he was made a consul) at the age of 49.

Marcius Rufus quaestor in castris relictus a curione ut in Siciliam navibus
referantur magistris navium imperat, tantus fuit omnium terror. Nihil harum rerum acciderat, itaque omnibus perterritis in scaphas conscendere quam
celerrime cuperent.
The quaestor Marcius Rufus, who had been left in the camp by Curio (a man named Curio, or a priest from the curia, I can't say), orders the commandants of the ships to sail back to Sicily, such was everyone's terror.

Or : Such was everyone's terror that the quaestor ... back to Sicily.

None of these ships had yet arrived so that everybody was terror-stricken
and wished to board the small craft as fast as possible.