Validating multiple form fields

I working on a plugin that enables users to use to two(2) different forms on either a post or page, that is, a custom login form and a application. combined I am looking at 10+ form fields to validate and make sure they are in the right data format (e.g.: text, password length, etc…)

Currently I am using two(2) separate functions for validation, both using the wp_error function (see code below), that is one for the login form and the other for the registration form.

//this function validates the login form
function validatedata($usr, $passwd){
	$errors = new WP_error();
	
	if(empty($usr || $passwd)){
		$errors->add('required', 'All Fields Required');
	}
	
	if(empty($usr)){
		$errors->add('usr_required', 'Please Enter Username');
	}
	
	if(empty($passwd)){
		$errors->add('passwd_required', 'Please Enter Password');
	}
	
	return $errors;
}

//this function validates the application form
function validateApp($firstName, $lastName, $phoneNum, $emailAdd){
	//accessing the WP_Error class via the global variable $appErr
	$appErr = new WP_Error();
	
	if(empty($firstName || $lastName || $phoneNum || $emailAdd)){
		$appErr->add('required', '*All Fields Required');
	}
	
	if(empty($firstName)){
		$appErr->add('required', '*First Name Required');
	}
	
	if(empty($lastName)){
		$appErr->add('required', '*Last Name Required');
	}
	
	if(empty($phoneNum)){
		$appErr->add('required', '*Phone Number Required');
	}
	
	if(empty($emailAdd)){
		$appErr->add('required', '*Email Address Required');
	}
	
	if(!empty($emailAdd)){
		if(!filter_var($emailAdd, FILTER_VALIDATE_EMAIL)){
			$appErr->add('invalid_format', '*Invalid Email Address');
		}
	}
	
	/*if(!empty($phoneNum)){
		if(!filter_var($phoneNum, FILTER_VALIDATE_INT)){
			$appErr->add('invalid_format', '*Phone Number must be a Number');
		}
	}*/
	return $appErr;
	
}