Excellent scene on a number of levels:

Fredo was the only one backing Michael up in his quest.

Sonny was yet again too quick to react to something.

Tom was stuck in the middle of them all.

Michael was adament that he wanted to be his own man and not follow into the family business.

etc.etc. Very clever scene cleverly reworked when Marlon Brando pulled out of filming at almost the last minute!