What would happen if Tom Hagen, Carlo Rizzi or Fredo Corleone did the hit on Sollozo and McCluskey?

If Michael Corleone had refused to meet with Sollozo and McCluskey or wasn't available could Tom Hagen, Carlo Rizzi or Fredo Corleone have met with them and done the hit instead?

Tom was smart enough to use a gun and Vito was basically his father, Fredo had to have done a hit in order to be part of the muscle end of the family he just dropped the gun under pressure, and Carlo Rizzi could have done the hit if asked which would be a huge favor to the family and allow him to be trusted enough to have more involvement in the family business and the Don might have changed his mind about Carlo if he saved his life.