Is there a way to get different Google calendars syncing with different Apple devices?
From my understanding you decide at  https://www.google.com/calendar/syncselect which calendars are to be synced with CalDav devices. No more, no less.

On the devices themself you can choose which calendars you want them to displayed. (It know this is quite trivial, but I do not quite see why this does not suffice).

Alternatively I would suggest creating mutiple Google accounts each one with its own CalDav syncing settings.
For each one you can decide which calendars are to be shared via CalDav. Each of your devices would be connected with one of these Google Account.
Then you share calendars among the Google accounts.

E.g.: Lets say A has all the calendars. You have an iPad and an iPhone. For each one create a google account (B and C). Now A shares the iPad related calendars with B and the iPhone related calendars with C. The iPad syncs with B, the iPhone with C.

It is not ideal but once set up it should run without any overhead.