That will work, but you need to be careful about how you wire up your power switch(s). You'll need individual circuits to power each of the contactor's coils otherwise you will run into problems.
So, you'll want something like this:
Also, you won't be able to switch on both contactors at the exact same time. So, for however long that delay is, that first contactor is going to be transferring all the amps, and these are startup amps so it'll be pulling more than normal operation.
It would be much simpler to just use one contactor. If you have individual chargers you don't have to worry about the batteries being unbalanced.