when you install wp change the table prefix of the db to something else instead of leaving it stock “wp_”. and do that for each install.
you change that in the wp-config.php file. i/e
// Change the prefix if you want to have multiple blogs in a single database.
//$table_prefix = ‘wpyour1stblog_’; // example: ‘wp_’ or ‘b2’ or ‘mylogin_’
then for your 2nd one- //$table_prefix = ‘wpyour2ndblog_’;