Yes. The daemons are able to see a merged view of these databases and will not differentiate between the entries coming from them.
No. An ephemeral database does not support features such as groups and validations.
Yes. Junos OS supports a maximum of eight instances of an ephemeral database. Before using these instances, instance names must be configured in the existing static database. There exists one "default" ephemeral instance that does not require prior configuration. Each ephemeral instance can be thought of as a private edit---that is, the configuration of instance1 would not be seen from instance2.
Note: There would be no sharing of instances. That is, if user-1 is editing ephemeral instance1, all other users are blocked from entering edit mode of instance1 unless user-1 releases it.
Yes. The configuration of all ephemeral instances would be synchronized to the backup Routing Engine for redundancy at commit synchronization time in dual Routing Engine systems. Similarly, ephemeral instances would be synchronized to all other Routing Engines present in multichassis and virtual-chassis systems.
Only a syntax check is performed for a commit in an ephemeral database for incoming ephemeral configurations. Because no commit check is performed, the semantics of the configuration would not be checked. It is recommended that you look at various system events such as the system log for feedback.