Greetings from Red Hat!!

1) How to add a group to the same file?

Create a file /etc/sshd.users and for group create a file /etc/sshd.group. Please enter the user name [one name each line] and the specific group names in the /etc/sshd.group
For example:
# vi /etc/sshd.users
test1
test2
test3

#vi /etc/sshd.group
group1
group2
group5

Save both the files and in /etc/pam.d/sshd add the following lines to the end of the file,
# vi /etc/pam.d/sshd
auth       required     pam_listfile.so item=user sense=deny file=/etc/sshd.users onerr=succeed
auth       required     pam_listfile.so item=group sense=deny file=/etc/sshd.group onerr=succeed