Luggage Storage at Train Stations

Hi,

We are a large family travelling with VERY large suitcases and we're hoping that at some points, we can store our really big suitcases in lockers or storage facilities of some kind while we sightsee some of the major cities.

Does anyone know if Okayama JR station and Hiroshima JR stations have really BIG lockers and/or a storage facility where we can place them for the day? I'm worried that lockers may be taken the day we need them so and we have at least 10 suitcases (travelling with extended family) so ideally if we could leave them somewhere, that'd be ideal.

Thanks