I think you might not need multiple loops to get your data into your template.

As I understood it, it’s a matter of sorting. You want to sort your posts so that posts with premium-franchisor set to 1 appear first. You can already do this using WP_Query. This is how your arguments array could look like:

$args = array(
    // Get all posts
    \'posts_per_page\' => -1,
    // Order by meta value first, then order by post date
    \'orderby\' => array(
        \'meta_value_num\' => \'DESC\',
        \'date\' => \'DESC\'
    ),
    // Select meta key which will be used for meta_value_num in orderby
    \'meta_key\' => \'premium-franchisor\',
);

Concluding from the title of your question I guess that you want to use Timber together with Twig to bring your data into your template.

This is how you could do that:

<?php

$context = Timber::get_context();

$args = array(
    // Get all posts
    \'posts_per_page\' => -1,
    // Order by meta value first, then order by post date
    \'orderby\' => array(
        \'meta_value_num\' => \'DESC\',
        \'date\' => \'DESC\'
    ),
    // Select meta key which will be used for meta_value_num in orderby
    \'meta_key\' => \'premium-franchisor\',
);

$posts = Timber::get_posts( $args );

$context[\'posts\'] = $posts;

Timber::render( \'archive-agency.twig\', $context );

In Timber you use a context that you fill with the data you want to hand over to your template. To set up all the basic data Timber needs, we use get_context() at the beginning. We then use Timber::get_posts() to basically do a normal WP_Query with our customized args. Getting your post through Timber will make it easier to access post properties in your template.

You could display your posts like this:

<div class="post-preview">
    <a href="{{ post.permalink }}">{{ post.title }}</a>
    <span class="post-date">{{ post.date }}</span>
    {% if attribute( post, \'premium-franchisor\') %}This is a premium post.{% endif %}
</div>

See, post.permalink or post.title are not properties you get when you run a normal WP_Query, but only if you query through Timber. Here you’ll find a list with methods and properties that you can use.

Using multiple loops in Timber

Since you asked how to do multiple loops, I will also show you an example of how you could achieve the same result you tried:

$context = Timber::get_context();

// Get all premium_posts
$premium_args = array(
    \'meta_key\' => \'premium-franchisor\',
    \'meta_value\' => \'1\',
    \'posts_per_page\' => -1,
);

$premium_posts = Timber::get_posts( $premium_args );

// Get all other posts
$my_other_args = array(
    \'meta_key\' => \'premium-franchisor\',
    \'meta_value\' => \'0\',
    \'posts_per_page\' => -1,
);

$my_other_posts = Timber::get_posts( $my_other_args );

// Merge the two post arrays into one and assign it to context
$posts = array_merge( $premium_posts, $my_other_posts );
$context[\'posts\'] = $posts;

Timber::render( \'index.twig\', $context );

When you get your posts through Timber, you don’t get an object that you have to loop over to get to your data, but you get a simple array of posts to work with. You can edit, extend, sort or in your example: merge them very easily.

A small remark on premium-franchisor

In your meta key premium-franchisor you used a hyphen. I’d advise you to use an underscore instead of a hyphen because often, it’s easier to access a property. E.g. you wouldn’t have to use

{% if attribute(post, \'premium-franchisor\') %}{% endif %}

But could just use

{% if post.premium_franchisor %}{% endif %}

Even if this is a very late answer, I hope this will help you or others get going with Timber and Twig.