Register Form for Specific Role

I have created two separate roles for my site, buyer and seller, with buyer as default role.

I was trying to make a specific register form for a specific role (seller). Email activation was used on registration.

I put this line on custom register-seller.php form, inside the <form> tag.
<input type="hidden" id="role<?php $template->the_instance(); ?>" name="role" value="seller" />

Then I add this on functions.php

function tml_user_register( $user_id ) {
	if ( !empty( $_POST['first_name'] ) )
		update_user_meta( $user_id, 'first_name', $_POST['first_name'] );
	if ( !empty( $_POST['last_name'] ) )
		update_user_meta( $user_id, 'last_name', $_POST['last_name'] );
	if (isset($_POST['role'])){
       $userdata = array();
       $userdata['ID'] = $user_id;
       $userdata['role'] = $_POST['role'];

       wp_update_user($userdata);
   }
}
add_action( 'user_register', 'tml_user_register' );

function set_role_on_registration( $user_id ) {
    if( isset($_POST['role']) )
        {
            $role = 'seller';
        }
    if ( in_array( $role, array( 'seller', 'buyer' ) ) )
        add_user_meta( $user_id, 'pending_role', $role );
}
add_action( 'tml_new_user_registered', 'set_role_on_registration' );

function set_role_on_activation( $user_id ) {
    if ( $pending_role = get_user_meta( $user_id, 'pending_role', true ) ) {
        if ( !in_array( $pending_role, array( 'seller', 'buyer' ) ) )
            return;
        $user = new WP_User( $user_id );
        $user->set_role( $pending_role );
        unset( $user );
    }
}
add_action( 'tml_new_user_activated', 'set_role_on_activation' );

So right now, even if a user register through seller’s register form, he always ends up as buyer after activation. Any help would be appreciated!

https://ww.wp.xz.cn/plugins/theme-my-login/