Don't be scared off by the "deacons bed" comment.
Yes the daybed is small and probably wouldn't accomodate your 9 y/o, but your 5 y/o may prefer it to sharing the pull out couch.
And while I'll agree that the daybed is no tempurpedic, the pull out couch mattress isn't anyting to write home about either.
The daybed is just another option that you would have IF they give you one. There is no extra charge so why not ask for it? Isn't the possibility of having this option better than having no option at all?
In the studios, if you don't have the daybed, its not like they put anything else in that space. In that scenario, both kids ARE on the couch.
At the very worst, if you request and get a daybed and your child "refuses" to sleep there, you'll have an extra place to sit down or put your bags if you don't use it as a bed.
After a full and fun day at the parks, my tuckered out son (and most kids) could probably sleep on a cement floor.
Enjoy, and have a great trip.