You can use for loop to untar multiple .tar.gz files to another folder. The following code will take /destination/folder/path as an argument to the script and untar all .tar.gz files present at the current location in /destination/folder/path.
if [ $# -ne 1 ];
then
echo "invalid argument/s"
echo "Usage: ./script-file-name.sh /target/directory"
exit 0
fi
for file in *.tar.gz
do
tar -zxvf "$file" --directory $1
done