You can install Banktivity on multiple Mac’s with one license. You do not need to purchase multiple licenses.

To share your Banktivity data among multiple devices you can use the Cloud Sync option available in Bankitvity.  Information about cloud sync has been posted in a separate Support Article here: https://www.banktivity.com/support/articles/ibank-5/how-do-i-use-ibank-cloud-sync-to-share-documents-between-my-devices/