Example organization of context files in Behat.

CustomerContext.php

<?php

use Behat\Behat\Context\BehatContext;

final class CustomerContext extends BehatContext
{
    // ... your step definitions related to customer
}

FeatureContext.php

<?php

require_once "PHPUnit/Framework/Assert/Functions.php";

use Behat\Behat\Context\BehatContext;

final class FeatureContext extends BehatContext
{
    public function __construct(array $parameters = array())
    {
        // customer context contains all the step definitions related to customer role
        $this->useContext('customer', new CustomerContext());
        // merchant context contains all the step definitions related to merchant role
        $this->useContext('merchant', new MerchantContext($parameters['merchant_id']));
    }
}

MerchantContext.php

<?php

use Behat\Behat\Context\BehatContext;

final class MerchantContext extends BehatContext
{
    private $merchantId;
    
    public function __construct($merchantId)
    {
        $this->merchantId = $merchantId;
    }
    
    // ... your step definitions related to merchant
}