If two tags in the middle i need comma

wp_tag_cloud() accepts a separator parameter, so you can modify your call like this:

wp_tag_cloud( array(
    'separator' => ", ",       // Default value: "\n"
    'unit'      => 'px',       // font sizing choice (pt, em, px, etc)
    'include'   => $tag_ids,   // ID's of tags to include, displays none except these
) );