Fuji kizaru combo in the sea would be an overkill for many pirate crews lol.
I don't think they could kill some strawhats thought.
Their attacks, even if the strawhats couldn't see the admirals they wouldn't hit the sunny.
Now if strawhats could see/sense them, the admirals would have a big problem.
Luffy alone would be quite troublesome, even for 2 admirals lol.
Yeah, it's not strictly the mugiwaras but most (every?) crews would be in deep shit.
Jinbei could get away, Sanji too. Maybe Usopp.
But then you have the Hammers: Luffy, Chopper, Robin, Brook that would be in great trouble.
Zoro, Franky and Nami are just normal humans in water and they lack blocking techniques like Bartolomeo or Mr3.
Best bet is to send Luffy and Sanji too fight them in the air, I agree. But that is only possible if they have CoO activated all the time so they can't get ambushed.