Is it possible to copy the snapshot(EBS or RDS) to other AZ's in the same region between two cross accounts?
Unlike EBS volumes and RDS instances, EBS snapshots and RDS snapshots do not exist in a single availability zone. Snapshots do not have a single AZ “home”. They exist in the region as a whole. So there is no concept of copying a snapshot from one AZ to another. A new EBS volume or RDS instance can be created in any AZ from the snapshot.
EBS and RDS snapshots can be copied to other AWS accounts and/or other AWS regions. But they cannot be copied from one Availability Zone to another Availability Zone. This is because they are not contained within an Availability Zone. When you have an EBS snapshot, you can restore an EBS volume from the snapshot into any Availability Zone.
Also, EBS snapshots and RDS snapshots are stored in Amazon S3. Amazon S3 replicates data across multiple data centers and multiple devices.