Act 2 Scene 4 What reasons do Ross and Macduff give for believing the innocence of the grooms and Duncan's sons?

Ross believed the grooms had no reason to kill Duncan, thus, it was a shame Macbeth had killed them.

"Alas, the day!

What good could they pretend?"

Ross also felt that it was unnatural for Duncan's sons to have committed the crime.

"'Gainst nature still!

Thriftless ambition, that will raven up

Thine own lives' means! Then ’tis most like

The sovereignty will fall upon Macbeth."