At one point Lady Macbeth talks about knowing the feeling of breastfeeding a child, so it is possible to assume that they do have children. However, in the play you never come in contact with any children of Macbeth.
Duncan and Macbeth are cousins. Therefore, they are bound by kinship. They are also bound by subject and host, as Macbeth is hosting Duncan as his guest.
In Act 3 Scene 1 Macbeth says: "We hear our bloody cousins are bestow'd In England and in Ireland, not confessing Their cruel parricide, filling their hearers With strange invention" Presumably, Duncan's sons are suggesting that Macbeth killed Duncan, not them.
why was macbeth releuctant to kill duncan
The night of Duncan's murder he is spending the night at MacBeth and Lady MacBeth's castle.
"I" said Macbeth, "with the servants' daggers. I killed Macbeth."
There is no indication of any closeness between them. Macduff is never much interested in socializing with Macbeth. We first see him when he arrives at Macbeth's castle to see Duncan. Note that it is the king he wants to see, not Macbeth. When Macbeth is named king, Macduff refuses to attend the coronation. He also refuses to come to Lady Macbeth's dinner party. It would appear that he never liked Macbeth much.
Macbeth was a loyal vassal of King Duncan. Macbeth's act should not be considered regicide.
Macbeth kills Duncan's grooms after Macduff discovers the body.
Macbeth kills Duncan in his own castle at night time.
They were killed by Macbeth because he blamed them for Duncan's murder.
Macbeth stabbed him when he was asleep.
The reaction between Lady Macbeth and Macbeth is initially very different after they kill Duncan. Lady Macbeth is enthusiastic but Macbeth regrets his actions.