"ORA-01017: invalid username/password" while connecting to an instance remotely as sysdba
Seems simply a password issue. Different instances may have different passwords, the SYS password is not necessarily the same for all the instances on the same server. Make sure remote_login_passwordfile is configured properly in the instances, and the password file exists for instance SID1 on the server in ORACLE_HOME/dbs/orapwSID1 (Linux-Unix) or ORACLE_HOME/database/pwdSID1.ora (Windows).

If you do not know the correct SYS password, you can recreate the password file, for example:

orapwd file=$ORACLE_HOME/dbs/orapwsid1 password=xxxx force=y