do you think the caporegimes were afraid of don corleone? He split them into two different boroughs when they were coming up in the life, and even tessio understands its a security issue and that the Don "didn't want his capos to conspire against him."

if one of the capos didn't follow an order of the don, would they be whacked? if they were old friends, and vito asked tessio to whack someone and he didnt, what do you think would happen?

i'm asking becuase i never really saw anyone (inside the family) deny the don, or flat out say they wouldnt do what he asked. would he kill one of them?

Vito was a murderer. He was sovereign over an empire that produced revenue for him from just about everything illegal, illicit, and immoral. I doubt that he had qualms about murdering anybody. In the novel, he expresses his inability to muder his son in law because he doesn't have the heart anymore. But that's near the end of his life. In his prime, he would have murdered anyone he thought he had to.

It's interesting that we see the capos only twice in the presence of Vito Corleone: At his sick bed (Sonny acts as the head of the family) and later when Vito has turned over his power to Michael. (I'm not counting the short moment where Vito dances with Connie.)

Which means we never see Tessio and Clemenza together with Vito as the head of the family!

Especially Clemenza acts very humbly in the fish tank scene. But also Tessio still seems to have a lot of respect towards Vito.

We also see the capos backing their don's play in the meeting with the Turk.
I don't doubt that Vito would eliminate anyone in the family if they were a threat.

But one of the paradoxes is that Vito usually didn't ask people (at least other men of respect) to do things that they couldn't do or didn't want to do on some level.

It's discussed in the book at greater detail but Tom notes that the only people who are absolutely 100% unafraid of Vito are Michael and Johnny Fontane.

Vito and his sons were cagey Dons when it came to giving orders. They knew their capos, and they probably would never give an order to one if they knew the capo either would not follow it blindly, or would have a hard time with it. When Vito did not want his people directly involved, he would call in a favor ("give this to a jew congressman from another district").
Michael was the same way He would nver have had Clemenza kill Tessio despite the betrayal. Clemenza and Tessio were lifelong friends who came up in the organization together. I believe Clemenza would have followed the order, but he might have reservations or regrets, so he had Hagen supervise it (Thus making Hagen think he might still have a shot at being a wartime consigliere) and Cicci do the deed. While Cicci worked for Clemenza, he saw this as an opportunity. There was a new Don, and the elimination of Tessio meant Cicci would have more access to the top, and more money. He had no loyalty to Tessio and was happy to prove himself to be a team player.

To the contrary, when it was necessary Sonny was smart to make Clemenza kill Paulie. Paulie worked for Clemenza, and to prove he was still a loyal capo, Clemenza had to fix the problem.

This is also why Mike gave Neri the order to kill Fredo. Neri was the most ruthless Capo he had....he was Michael's Luca Brasi. He would not have given it to Rocco, who might have a second thought.