The aside to Tom is a offhand admission that Tom is not as stupid as Michael thinks he is. It also could indicate that Fredo had already tried calling Tom and Tom told Michael or Michael would just figure Fredo would get in touch with Tom.

In the boathouse I still think that Fredo still had a tiny chance (perhaps a 1 in a 1,000,000,000 chance) to escape the full force of Michael's wrath if he had almost literally turned on his back and bared his throat. But no, he lost his temper, showed his deep resentments and also revealed he knew more about Roth's plans than he had let on. That did it.

I don't think Michael or Tom or any of the employees would have told Connie anything. But she's been around; she can pick up cues, especially from people she grew up with. I don't think she had any idea of what Fredo had actually done or the fact that Michael was planning his murder. She just wanted things to be good again. She knew her brothers were angry and wanted to make peace.