It is difficult to make much of a judgement about Edward, who does not have a speaking role in the play. He is only mentioned in the third person, as a king that has been hospitable to Malcolm in his exile. Malcolm also describes Edward's ability to cure the skin disease scrofula with the "royal touch." This was a common folk belief in Shakespeare's own day, and the monarchs of England made a ceremony of laying hands on scrofula sufferers each year. So we might say that the king of England is portrayed as a pious man who fulfils his obligations as monarch. Where Macbeth destroys lives, he uses his power to sustain them.

As for Duncan, there is little doubting that he is a good king and a decent man. Macbeth himself acknowledges as much when he is debating whether to kill the monarch:

...this Duncan 
Hath borne his faculties so meek, hath been 
So clear in his great office, that his virtues 
Will plead like angels trumpet-tongued against 
The deep damnation of his taking-off...

Duncan also trusts and holds Macbeth in very high regard, which makes Macbeth's treachery all the more horrible. Malcolm is portrayed as a noble figure. While he prudently flees Scotland, we learn on Macduff's visit to him in Edward's court in England that he is committed to avenging his father's murder. At the end of the play, with Macbeth dead, Malcolm is a decisive and strong leader. All three kings, then are portrayed as virtuous and good, a stark contrast with the wicked Macbeth.

In Macbeth, how are the murders of Duncan, his guards, Banquo, and Macduff's family similar?

Essentially, the similarities between the deaths of Duncan, his guards, Banquo and Macduff'f family, as seen in William Shakespeare's Macbeth, have one resounding tie: they all lose their lives based upon Macbeth's ambition.

Duncan and his guards die for one reason: Macbeth desires the crown. Since hearing the prophecy of the witches, Macbeth's ambitious nature has compounded. He will no longer allow fate to make the moves:

If chance will have me king, why, chance
may crown me
Without my stir. 

The guards die so that Macbeth can place blame on someone other than himself. Duncan dies so that Macbeth can have the throne.

As for Banquo's and Macduff's family, their murders are a part of Macbeth's plan to keep the throne. Macbeth knows that Banquo is a threat based upon the fact that he witnessed the prophecy. Known by readers but not by Macbeth, Banquo does believe that Macbeth may have had something to do with Duncan's death.

Thou hast it now: King, Cawdor, Glamis, all,
As the weird women promised, and I fear
Thou play'dst most foully for't.

Also, Macbeth fears that another part of the prophecy will come true: Banquo's sons will be kings. By this, Macbeth believes that he will lose the throne to Banquo's sons. Therefore, by trying to murder Fleance, and murdering Banquo, the likeliness of the prophecy coming true is lessened.

Like Banquo's murder, the murder of the Macduff family is meant to insure Macbeth keeps the crown. He believes that Macduff will try to kill him (again foreseen by the prophetic witches and the apparitions).

Macbeth! Macbeth! Macbeth! Beware
Macduff;
Beware the Thane of Fife. Dismiss me. Enough.

Therefore, Macbeth sends the murderers to kill Macduff (unaware that he has fled). Instead, the murderers kill Macduff's family.

Sinful Macduff,
They were all struck for thee! Naught that I am,
Not for their own demerits, but for mine,
Fell slaughter on their souls. Heaven rest them now!

In the end, all of the characters (Duncan, his guards, Banquo, and Macduff's family) are murdered to insure the throne for Macbeth.

In Shakespeare's Macbeth, how are Macbeth, Macduff, and Banquo similar?

They are all used to battles, and they all possess the fighting spirit. Macbeth and Banquo first show up at the beginning of the play from the battle against Norwegians in which they were successful. Everyone praises them for their valiance. Macduff is also capable of being a great warrior, such as when he kills Macbeth, as the end of the play shows.

They all exhibit confusion and have difficulty choosing a path to follow. Macbeth unsuccessfully grapples with his unchecked ambition, intensified by the witches' prophecy. Banquo's mind is also fixed on the witches' prophecy; however, he does not do anything about it, unlike Macbeth. And, Macduff exhibits tension between his duty as a husband and a father and his responsibility to save the country from a cold-blooded tyrant.

Good question. They are all warriors, and warriors of great power. They are brave and battle-tested. They all believe in omens or signs that in part determine their fate or safeguard them from danger. They all have to deal with guilt over what they do, and all are concerned with what it means to be an honorable man.

How do Macduff, Macbeth, and Banquo differ from each other?

First, it will be helpful to examine of each of these characters as individuals.

MACBETH - Macbeth is the central character of the play. Before arriving onstage, he is described as being brave and able to cut a man from "nave to th'chops" (I.i.24). Whether or not this description can be trusted, it is clear that Macbeth is believed to be a very strong and courageous warrior. At the beginning of the play, Macbeth listens to those around him and shows great charisma. However, Macbeth becomes a very ambitious and greedy character. His vaulting ambition drives him to commit murders in the play, and this ambition is ultimately his downfall. 

MACDUFF - Macduff is a Scottish noble and is often described as Macbeth's foil. Similarly to Macbeth, Macduff is a warrior. However, Macduff publicly feels emotions and is seen as a relatable character, specifically when his family is murdered and he becomes quite emotional. He is a character of great humanity and he often makes decisions based on his values and his honor. He does not profess empty rhetoric. Macduff can be trusted.

BANQUO - Banquo is an extremely likable character. He shows restraint and is suspicious of the witches. Banquo is loyal to Macbeth and he is kind to his son, Fleance. Banquo is one of the few characters the audience sees parenting a child, and so Banquo becomes one of the central father figures in the play. 

Macduff and Macbeth are the most obviously different. Macbeth frequently announces lies and coerces and deceives. Macduff, however, is true to his word. He does not state things he does not know to be true. Both of these men are warriors. Banquo, while also a fighter, is the most relatable character out of the three. He is not prone to hysteria, and he is more loyal than ambitious. 

How are Macbeth and Banquo similar and different in Shakespeare's Macbeth?

Macbeth and Banquo in William Shakespeare's Macbeth are similar in being good friends who are both successful Scottish generals in the army of King Duncan. They are also both ambitious. When Banquo and Macbeth meet the three weird sisters on the blasted heath, both are initially interested in listening to them, but Banquo recoils from them as evil supernatural beings but Macbeth allows himself to be influenced by them. There is some debate as to whether Banquo was complicit with Macbeth in the death of King Duncan. Even though he did not kill Duncan, he may have been complicit in knowing of it and keeping silent. However, Macbeth, in his murder of Duncan, then of Banquo, and then his subsequent reign of terror is obviously morally worse (whether simply by opportunity and intent is uncertain).