The quote, "For certain she is dead, and by strange manner" appears in Act 4, Scene 2. Messala brings Brutus news that his wife Portia has committed suicide. The "strange manner," according to Plutarch, was by swallowing hot coals. Brutus tells Cassius "...she fell distraught, / And, her attendants absent, swallowed fire." When Messala brings Brutus news that his wife has died, Brutus already knows it but evidently pretends that this is the first time he has heard about it.
The quote, "All that served Brutus, I will entertain them," occurs almost at the end of the play in Act 5, Scene 5. Octavius shows magnanimity, generosity, and wisdom in taking into his service men who had been his enemies during the battle that has just ended. He believes that the men who served Brutus with such loyalty and devotion will make good servants to himself. He is also asserting his feeling of power and authority as a conquerer and co-ruler of the Roman empire. Although Octavius is still quite young, he demonstrates that he has the potential, especially the practical intelligence, to be an effective leader and eventually to become emperor and sole ruler.
In Shakespeare's Julius Caesar—with regard to your quote from Act V, scene v—there may be several explanations for Octavius' decision to "entertain" Brutus' followers.
First, the quote:
All that served Brutus, I will entertain them. (66)
This means Octavius (Caesar) is granting amnesty (a pardon) to Brutus' men.
However, in the previous scene with Antony, analysis offers commentary regarding Antony's similar actions; this presents the reader with "food for thought" about the motivation behind Octavius' decision to spare Brutus' men. The eNotes analysis for scene four notes...
But Antony recognizes [Lucilius] and tells his soldiers, “Give him all kindness. I had rather have / Such men my friends than enemies.” (Sc. 4, 29–30) Antony seems to be recruiting allies for a future clash with Octavius.
Antony, who was quick to condemn Brutus as being overly ambitious—and who manipulated the crowds after Caesar's assassination against Brutus and his co-conspirators—is really the ambitious one. Whereas Brutus killed Caesar for the sake of Rome, Antony wants to rule Rome and has never had the honorable intent that Brutus had. Brutus was willing to sacrifice his life in order to save his beloved Rome from the danger he felt if Caesar was crowned "king." Antony is really nothing more than a charismatic politician with a desire for power.
So Antony, the analysis says, offers kind treatment of Lucilius, who is trying to pass himself off as Brutus in order to give Brutus more time to escape. Antony praises Lucilius as Brutus' equal (nonsense!) and tells his soldier to treat him well: better that he be a friend than an enemy.
This is not Brutus, friend, but, I assure you,
A prize no less in worth. Keep this man safe,
Give him all kindness; I had rather have
Such men my friends than enemies...(V.iv.27-30)
Acknowledging that there might be a time that Lucilius would be a valuable friend rather than a dangerous enemy shows that Antony is a forward-thinking man planning to take the throne (at some point) from Octavius.
I mention this with a consideration of whether Octavius is contemplating the same need of future support by offering amnesty to Brutus' followers. You ask what Octavius' words say about him. This is where I believe we can separate the kind of man Antony is from the true caliber (degree of excellence) of Octavius.
Octavius pardons Brutus' followers, I believe, for two reasons. First, he understands and appreciates the dedication of loyal soldiers to their leader. (The value of loyalty here cannot be understated.) Second, while Octavius may have censured Brutus' actions in murdering Caesar, his words show us that he respected Brutus for his unselfish motivation—every action Brutus took was not for personal gain, but for the good of Rome. This is, of course, what makes Brutus a true hero. (We may still grapple with the ethical ramifications of killing Caesar: "ethical regicide" was a moral dilemma not unknown during Shakespeare's time). Second, this action will reunite war-torn Rome. It would seem Octavius, like Brutus, cares for the good of Rome.
Antony delivers famous lines regarding what a noble Roman and "real" man Brutus was—lovely though perhaps empty words, but Octavius honors Brutus—the soldier and patriot—with what seems to be genuine respect.
According to his virtue let us use him...
Within my tent his bones tonight shall lie,
Most like a soldier, order'd honorably. (82, 84-85)
Im Truly Sorry, But I meant the quote: "All that served Brutus, I will entertain them"