PostgreSQL-v13-Repmgr: Split-Brain issue

Hi,

I have PosgreSQL primary and a local standby(same data center) and a remote
standby for DR purposes. Currently repmgr is enabled on the same servers
for an automatic failover but it's running into split brain issues.

I have two questions:

1. In order to avoid split-brain between primary and local standby, can
repmgr be set up on a separate witness node to help provide fencing or
prevent a split brain?
2. If so, can I use the same witness server for multiple sets of primary
and secondary postgresql servers/clusters? like one witness server for one
environment that can have multiple postgreSQL clusters? Is there any
document available for that configuration?

Thanks
Amit