It seems like the aav's are only high enough to make it difficult for the Oilers, not that they'd actually let these guys go.
It's a double offer-sheet, which is a strategy that is sometimes discussed with NHL analysts.
Two overpaid players for a cap strapped team makes it more difficult to match. There is no guarantee that the Blues really want both guys. I suspect they probably really like Broberg, because you don't risk losing 9M of cap space over 2 years that you don't actually want to pay.
I suspect they think that the Oilers will match Dylan Holloway, who comes in at slightly overpaid based on his resume, but still tolerable, but won't match Broberg, who received a Kotkaniemi style overpayment, relative to his role this past two seasons on the Oilers.
It is can't lose for the Blues. If the Oilers match, a conference rival has to deal from a huge position of disadvantage cap wise. If the Oilers do not match, the Blues get two good young players for only a 2nd+3rd and cap space for 2 years.
People talk about trading Ceci, but the Oilers are now dealing from a very bad position. Teams recognize leverage. There isn't a lot of cap flexibility this late in the off season, and most teams who do have cap flexibility are budget teams. I think it is going to be harder than expected.
I could see something like Ceci and a draft pick to Utah for Weber's contract, then Utah could flip Ceci to a third team if they don't actually want him. Maybe Detroit would take Ceci, since they were after a RHD in Trouba earlier in the offseason and have cap space.