They do...but only especially after Goku told them ["there's no telling how strong he might be when he really gets going] when he visited Cell in the ring. Keep in mind this is before Goku powered up to 50% power for Karin.
I think that could be explained by Cell being at the level he was initially, before doing that silent power up against Vegeta. The initial level to which #16 states Vegeta is still superior in everything:
Chapter: 382 (DBZ 188), P11.1-4
No.16: “Cell really did get considerably stronger…But Vegeta’s still better than him at everything!”
Vegeta: “Damn you. You’re not taking this seriously.”
Cell: “I told you I was warming-up.”
Since nobody but Kuririn [who had been kicked] could tell how much more powerful Cell could get, then it stands a reason Goku could only make guesses.
Of course my guess is once the fight was over Vegeta/Trunks/Kamiccolo etc realize this is not his full power though..since Cell flat out says he's just warming up
In reality, what Cell defined as "warm up" was the level he was using initially against Vegeta, the one who #16 read initially and stated was < Vegeta.
This is the level defined as "warm up". The level in which he tooled Vegeta was the one defined as "serious Cell":
This we know is a lot stronger than Cell's warm up power. Since Trunks was like "I was afraid he could be that strong"
That was a Viz error. That's what is said, in reality:
That's direct from the Orange Bricks, translated by Steve Simmons. Trunks only questioned Goku's words, the "Is that strong?" was something Viz added up.
Now if 50% Goku = warm up Cell..would they not immediately say that Goku is going to get killed? Since they know Cell can get way stronger? Or do they at least have faith in Goku to put up a fight?
I think the idea of 50% = warm up Goku holds water due to it being still in the same realm of warm up Cell. Goku flat out stated he can't exactly tell how strong Cell would become if he gets down to business and that he won't know until he tries, that is, it's all guesswork. If Goku's level showcased at Karin blows warm up Cell out of the damn water, then I'd sure expect them at least questioning Goku's word, since it didn't pass from a guess in Goku's part, to begin with.
I agree with your "Trunks is surprised with Kamiccolo being fodder" though. That's where I think the idea of Trunks expecting Goku being still the top dog, despite being > 50%, comes from. I also think Vegeta realized it, since his line right before Goku fighting implies it, but he is still confident nevertheless, since he surpassed the power Goku showed at Karin, that is, he overcomed the minimum requirement to show confidence, kind of like Piccolo showed confidence going up against the androids, since he surpassed Yardrat Goku and Mecha Trunks, but still had a bad gut feeling or so.