Yes i am able to shut and start all 4 DBs manually.
Attached below is my oratab file :-
# This file is used by ORACLE utilities. It is created by root.sh
# and updated by the Database Configuration Assistant when creating
# a database.
# A colon, ':', is used as the field terminator. A new line terminates
# the entry. Lines beginning with a pound sign, '#', are comments.
# Entries are of the form:
# The first and second fields are the system identifier and home
# directory of the database respectively. The third filed indicates
# to the dbstart utility that the database should , "Y", or should not,
# "N", be brought up at system boot time.
# Multiple entries with the same $ORACLE_SID are not allowed.
Sorry, what i meant what press enter-key on the last DB list in the oratab file and create a empty new line in the oratab file after the last entry in the oratab file. When i issue dbstart and dbshut again, it will able to shut and start all DB in oratab file.