$dbh = new Dsn;
$pdo = $dbh->connnect1Read(NAME1, USER2, PASS2);
$pdo2 = $dbh->connnect2Write(NAME1, USER1, PASS1);
$pdo3 = $dbh->connnect3(USER2, PASS2);
$pdo4 = $dbh->connnect4(USER3, PASS3);
$pdo5 = $dbh->connnect5(USER4, PASS4);

class Dsn
{

 private $host = 'localhost';
 private $charset = 'utf8mb4';

 private $dbName1;
 private $userName1;
 private $userPass1;

 private $dbName2 = 'db2';
 private $userName2;
 private $userPass2;

 private $dbName3 = 'db3';
 private $userName3;
 private $userPass3;

 private $dbName4 = 'db4';
 private $userName4;
 private $userPass4;


 private $opt = [
                            PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
                            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
                            PDO::ATTR_EMULATE_PREPARES   => false,
                      ];


  public function connnect1Read($dbName, $userName, $userPass)
  {
    $this->dbName1 = $dbName;
    $this->userName2 = $userName;
    $this->userPass2 = $userPass;

    $dsn = "mysql:host=" . $this->host . ";dbname=" . $this->dbName1 . ";charset=" . $this->charset . "";
    $pdo1 = new PDO($dsn, $this->userName2, $this->userPass2, $this->opt);

    return $pdo1;
  }

  public function connnect2Write($dbName1, $userName, $userPass)
  {
    $this->dbName1 = $dbName1;
    $this->userName1 = $userName;
    $this->userPass1 = $userPass;

    $dsn = "mysql:host=" . $this->host . ";dbname=" . $this->dbName1 . ";charset=" . $this->charset . "";
    $pdo2 = new PDO($dsn, $this->userName1, $this->userPass1, $this->opt);

    return $pdo2;
  }

  public function connnect3($userName, $userPass)
  {
    $this->userName2 = $userName;
    $this->userPass2 = $userPass;

    $dsn = "mysql:host=" . $this->host . ";dbname=" . $this->dbName2 . ";charset=" . $this->charset . "";
    $pdo4 = new PDO($dsn, $this->userName2, $this->userPass2, $this->opt);

    return $pdo3;
  }

  public function connnect4($userName, $userPass)
  {
    $this->userName3 = $userName;
    $this->userPass3 = $userPass;

    $dsn = "mysql:host=" . $this->host . ";dbname=" . $this->dbName3 . ";charset=" . $this->charset . "";
    $pdo5 = new PDO($dsn, $this->userName3, $this->userPass3, $this->opt);

    return $pdo4;
  }

  public function connnect5($userName, $userPass)
  {
    $this->userName4 = $userName;
    $this->userPass4 = $userPass;

    $dsn = "mysql:host=" . $this->host . ";dbname=" . $this->dbName4 . ";charset=" . $this->charset . "";
    $pdo3 = new PDO($dsn, $this->userName4, $this->userPass4, $this->opt);

    return $pdo5;
  }
}

function connnect($dbName, $userName, $userPass)
{
    $host = 'localhost';
    $charset = 'utf8mb4';
    $opt = [
                        PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
                        PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
                        PDO::ATTR_EMULATE_PREPARES   => false,
                  ];
    $dsn = "mysql:host=$host;dbname=$dbName;charset=$charset";
    return new PDO($dsn, $userName, $userPass, $opt);
}

$dbRead = connnect(NAME1, USER2, PASS2);
$dbWrte = connnect(NAME1, USER1, PASS1);
$db3 = connnect(NAME3, USER2, PASS2);
$db4 = connnect(NAME4, USER3, PASS3);
$db5 = connnect(NAME5, USER4, PASS4);