Certificates

When having more than one app, do i need a keystore for each app and each keystore with the key for that app, or should i have only one keystore with the keys for each app. I’m asking because i would like to know what’s the better path to take if later i would need to change app ownership and i would need to provide the other party with the app certificate in order for them to be able to update the app in the future. If i have only one keystore is it ok to export that one app’s key and then be able to use that key to update that app independent from the others, possibly importing the key into another keystore.

Thanks.