Surprisingly little. After killing Duncan, his feelings seem to have been numbed so that he does not feel any remorse for his killings. He does feel fear, however, which killing more people only makes worse. On the other had he says to Macduff, "my soul is too much charged with blood of thine already" which suggests that even at this late date, he feels some remorse about the murders.
Lady Macbeth does not convince Macbeth to kill Macduffs family. She convinces him to kill the King at the start of the play, but after that she has no input in the decisions he makes. Macbeth chooses to have Macduffs family killed so that he may seize the Macduff castle for his own. The witches also tell him to 'beware Macduff' when he visits them and so he feels threatened by him. Macbeth doesn't actually personally kill Macduffs family either, he hires the same thugs that he hires to assassinate Banquo and Fleance to murder him.
Because Macbeth believes in the prophecies so much, he thinks that he is safe because that is what the witches want him to think. The witches tell Macbeth to beware of Macduff, even though Macbeth thinks he is safe he wants to make sure he iscompletely safe so he decides to kill Macduff and his family but only suceeds in killing Macduffs family not Macduff, and the Macduff takes revenge and kills Macbeth.
Macbeth sends murderers to kill Macduff's family in an attempt to eliminate any potential threats to his own power. This ruthless act solidifies Macbeth's descent into tyranny and cruelty, as he seeks to maintain his position on the throne at any cost. The murder of Macduff's family ultimately leads to Macduff seeking revenge against Macbeth, contributing to his downfall.
It's a two-part answer. One, Macbeth is a traitor and killed the King of Scotland. Macduff is loyal to the rightful heir, Malcolm. Macduff assists Malcolm in the retaking of Dunsinane castle and murders Macbeth. But Macbeth also hired assassins to have Macduffs family murdered. Macduff's wife and children were all murdered after he fled to England with Malcolm.
Macduff challenges Macbeth to a duel towards the end of the play "Macbeth" by William Shakespeare. Macduff seeks revenge for the murders of his family that Macbeth ordered. The duel results in Macduff killing Macbeth and ultimately ending his reign as king.
Macduff seeks revenge on Macbeth as a result of his family being murdered by Macbeth. Malcolm seeks revenge on Macbeth in order to regain his crown and avenge his fathers murder (an act of regicide). Banquos ghost seeks revenge on Macbeth as a result of his own murder (however this shows a blurring of boundaries between reality and fantasy because Macbeth is the only person to see the ghost it is unclear as to whether or not this was a hallucination as a result of his madness).
Macduff's relationship with Macbeth is adversarial. Macduff seeks to avenge the murder of his family, which Macbeth ordered, by confronting and ultimately killing Macbeth. Macduff is a key figure in Macbeth's downfall.
Killing Macduff's family causes Macduff to become more determined to seek revenge on Macbeth, as it increases his personal vendetta against him. This act also leads Macduff to join forces with Malcolm and the English army to overthrow Macbeth's tyrannical rule.
1. Macbeth 2. Lady Macbeth 3. Witch One 4. Witch Two 5. Witch Three 6. Banquo 7. King Duncan 8. Macduff 9. Malcolm 10. Hecate 11. Fleance 12. Lennox 13 The first murderer that kills Banquo 14. The 2nd Muderer that kills Banquo 15. The Murderer that kills Macduffs Family 16. Porter 17. Lady Macduff 18. Donalbain
Lady Macduff thinks her husband has left because he is a traitor and has abandoned them. She feels betrayed and abandoned, which causes her to question his loyalty and commitment to his family.
Malcolm is convinced of Macduff's loyalty when Macduff reveals his grief over the deaths of King Duncan and his own family at the hands of Macbeth. Macduff's genuine sorrow and commitment to seeking justice for these atrocities proves to Malcolm that he is a trustworthy ally in the fight against Macbeth.
Macbeth didn't think Macduff was a threat because the witches said "None of woman born shall harm Macbeth." Macbeth welcomes this good news and, assuming Macduff was born the natural way, Macbeth thinks he has nothing to fear.