Nonus (9) and Decimus (10) are some you've missed, and the original "8" name was Octavius not Octavian. Octavianus (anglicised as Octavian) is the adjectival form of Octavius.

The numbers 1 to 4 (Primus, Secundus, Tertius, Quartus) also appear as names, but only later in Roman history.

It should be noted that these names are ordinal numbers- that is, they translate as "fifth", "sixth", etc. It is often suggested that they refer to the child's position in birth order, and this may have originally been true. However, not every Decimus was a tenth son (or tenth child)- for instance, there were eight consuls called Decimus Junius Brutus, including at least one set of grandfather, father and son. It's extremely unlikely that all of these were tenth sons! A much more plausible explanation is that it had simply become a popular name in that family.

See GD Chase, The Origin of Roman Praenomina, in Harvard Studies in Classical Philology (1897)