Android - Multiple db.crypt12 databases in the whatsApp Databases folder

These are just database backups. WhatsApp generates a backup and stores it to the WhatsApp folder on your storage. See the WhatsApp FAQ:

• Your phone will store up to the last seven days worth of local backup files.
• Local backups will be automatically created every day at 2:00 AM and saved as a file in your phone.

Thereafter, if you have enabled backup to cloud, WhatsApp will also upload a copy of this backup to the Google Drive. If at some point you need to re-install WhatsApp, the app will restore your messages and data from these backup files.

Now coming to the list of databases that you see, notice the date in each of the database files, except the first. Every night when a new backup is generated, it is saved as msgstore.db.crypt12. The backup from the last day is renamed with a date in the name.

WhatsApp keeps a backup of 7 days + the current main backup. It keeps on deleting the older backup files as new ones are generated every night.

You can delete them all and that will have no issues on the functionality of your WhatsApp app. That said, it is kinda useless to delete as new ones will again be generated every night and within a week you'll once again have these 7 files saved in your phone's storage.

And as of now, WhatsApp does not give you an option to choose how many backup files to keep.