what command can i use to tell if a script is running under different users?

ps -e -o"user,args" | grep <scriptname> | nawk '{ print $1 }' | sort -u
Maybe you have to replace "nawk" by "awk" depinding on your system.

example:
ps -e -o"user,args" | sc[r]ipt.sh | nawk '{ print $1 }' | sort -u

Put 1 letter of the <scriptname> between "[" and "]".
That way the "grep" itself will not be part of the result.

Compare e.g.
# ps -ef | grep sshd
user3 306 1 0 Feb 09 ? 0:16 /usr/lib/ssh/sshd
user2 14740 14733 0 17:25:44 ? 0:06 /usr/lib/ssh/sshd
user1 14733 306 0 17:25:43 ? 0:00 /usr/lib/ssh/sshd
user2 23404 14773 0 21:46:36 pts/1 0:00 grep sshd

or
# ps -ef | grep ss[h]d
user3 306 1 0 Feb 09 ? 0:16 /usr/lib/ssh/sshd
user2 14740 14733 0 17:25:44 ? 0:06 /usr/lib/ssh/sshd
user1 14733 306 0 17:25:43 ? 0:00 /usr/lib/ssh/sshd

effectively "ps -ef | grep ss[h]d" will do the same as "ps -ef | grep sshd | grep -v grep"