Plugin and themes are adding the same stylesheets

You can use wp_dequeue_style() to remove CSS a plugin is adding.

You can use it to dequeue the 2 stylesheets coming from your plugin and just keep the one in your theme.

However, they appear to be different versions of Font Awesome so you may run into some issues there, I’m not sure I don’t use Font Awesome.

Here is an example of wp_dequeue_style() which you can edit and add to your theme’s functions.php.

function wpse_remove_styles() {
   wp_dequeue_style('dokan-fontawesome');
}
add_action( 'wp_print_styles', 'wpse_remove_styles', 100 );

Note: You will need the handle for the stylesheet, which you can usually get by viewing the source, finding the stylesheet ID and removing -css. For example, in your case…

<link rel="stylesheet" id='dokan-fontawesome-css' href="https://wordpress.stackexchange.com/questions/354968/.vendors/font-awesome/font-awesome.min.css?ver=2.9.10" type="text/css" media="all" />

The handle should be dokan-fontawesome.