What, if anything, is going on at the start of the scene?

(1) Frankie and Cicci get out of the car. There's extra guys guarding the front of the house. Frankie asks "What's up?" and they gesture toward Bussetta, right at the front door. Frankie sighs and says, "We got company, huh?" and he advances on Bussetta;

(2) Frankie reaches Bussetta, who keeps his hands in his pockets, lowers his head, and does a quarter turn away from Frankie;

(3) Frankie walks past Bussetta into the house. His wife meets him at the door. Frankie asks in Italian something like "Who's here?", and she finally tells him Michael Corleone. Their daughter comes down the stairs at that moment, and follows as they chatter toward the study.

The wife and daughter I understand: a surprise visit from Michael Corleone is a rare and impressive thing. The rest of it, though, is it all just false mystery-building? Frankie's men are forbidden to speak Michael's name? Does Frankie know Bussetta, or why does he walk into the house without knowing who's in there?

Pete, it is something of an odd scene. I always wondered why Michael's bodyguard was left outside in the cold. Since Frankie was apparently at war with the Rosottos, I can understand the Frankie's bodyguards being left outside.

One other thing about that scene. Did you notice that as Frankie is exiting his car, there's something missing in the background. Figure out what it is? It's the wall that surrounded the compound in GFI.

It is kind of an odd scene, Pete. I think Buscetta waiting outside was Michael's way of putting Mrs. Pentangeli at ease--he's a pretty scary looking guy. And, if he'd gone in with Michael, probably some of Frankie's bodyguards would have had to come in, too.

Buscetta enters the story out of nowhere. But, he would have had to have had some connection with the Corleones to turn up on such short notice (the train scene). Frankie spotting him and saying, "We got company" affirms that he was a known commodity.

Oli, good catch about the wall. I also didn't think Frankie's office looked much like Vito's in the Connie wedding scene.

Buscetta was outside for Roth's visit too

I've always assumed that Buscetta is one of Don Tommasino's men, Michael drawing support from the one well that he is sure he can trust. In the scene where Vito kills Don Ciccio, Don Tommasino is shot, and the driver and another man, seemingly useless to the plan, get out of the car and help carry Tommasino to safety. I've wondered if that fourth man isn't young Buscetta, although it could just be that Coppola thought that carrying Tommasino looked cooler than dragging him, and that required an extra man.

Surprise here is Mrs. Pentangeli knew Michael Poor scared women, worried, having him in their house for half an hour, on their own
Also what is Buscetta going to do with a coat hanger and a pillow

Wonder whom Frankie thought was the "company"

Rosato brothers

The Rosato brothers took Mrs. Pentangeli and their daughter hostages!