Expected result see Oracle document - Oracle Data Guard Broker 11g Release 2 (11.2) E17023-06
9.5.1 Problems Starting the Observer
"Only one observer can be observing the broker configuration at any given time. If you
attempt to start a second observer, one of the following errors is returned:
ORA-16647: could not start more than one observer
DGM-16954: Unable to open and lock the Observer configuration file"
You only need one Observer, just configure the second set of databases.