Shamim's Plugins

Please follow https://www.shamimsplugins.com/support/topic/can-we-rename-message-box-to-inbox/#post-11735

add following code in your theme’s (child theme’s if you are using) functions.php

add_filter( 'fep_filter_user_name', function( $name, $id ){
	if ( $name ) {
		$name .= " ($id)";
	}
	return $name;
}, 10, 2);

Please see https://www.shamimsplugins.com/support/topic/allow-only-admin-to-message-groups/#post-36544

Keep unchecked that box.
Then add following line after add_action( ‘fep_display_after_announcement’, array( Fep_Read_Receipt::init(), ‘display_read_receipt’ ), 99 );

add_action( 'fep_display_after_message', array( Fep_Read_Receipt::init(), 'display_read_receipt' ), 99 );

Please go to Front End PM PRO > Settings > Recipient and uncheck “Can send to group”

Please remove first add_action( ‘fep_display_after_announcement’, array( Fep_Read_Receipt::init(), ‘display_read_receipt’ ), 99 ); line

You can use #fep-notification-bar to add any css to notification bar.
Try adding following code in Front End PM PRO > Settings > Appearance > Custom CSS

#fep-notification-bar {
    position: fixed;
}

You can try https://www.shamimsplugins.com/docs/front-end-pm/shortcode/fep_shortcode_message_to/ shortcode