No, you can't cluster a BizTalk Branch server, and what you are suggesting would breach the licencing. The branch licence just allows you to set up a stand alone server at a remote location, i.e. a Branch Office, that connects to the central Enterprise BizTalk Server .
BizTalk Server 2020 Licensing Datasheet
Editions Overview
BizTalk Server 2020 offers four editions:
• Enterprise Edition for customers with enterprise level requirements for high volume, reliability and availability
• Standard Edition for organizations with moderate volume and deployment scale requirements
• Branch Edition for hub and spoke deployment scenarios
• Developer Edition for testing and development use in conjunction with any of the above three editions.
BizTalk 2020 Licensing Models
- BizTalk Server 2020 Branch or Standard Edition software may not be installed on a server that is part of a networked cluster or in an OSE that is part of a networked cluster of OSEs on the same server.
- BizTalk Server 2020 Branch Edition software may only be installed on servers at the endpoint of its internal network (or edge of its organization) to connect business events or transactions with activities processed at that endpoint, provided, the server does not:
• act as the central node in a “hub and spoke” networking model,
• centralize enterprise-wide communications with other Servers or devices; or
• automate business processes across divisions, business units, or branch offices.
Use of BizTalk Server Branch edition requires BizTalk Server Enterprise Edition be installed