Adding an existing node as a translation
You can do this in code by reading the field values from the three translated nodes and add them as translation to the english node:

$node_en-&gt;addTranslation($langcode1, $node1-&gt;toArray());
$node_en-&gt;addTranslation($langcode2, $node2-&gt;toArray());
$node_en-&gt;addTranslation($langcode3, $node3-&gt;toArray());
$node_en-&gt;save();


This is for demonstration only, you can loop through the languages and get the langcode from the node.

The problem is that at the moment the translated nodes and the english node have no connection in the database. If you have some data in the nodes that do match, you can do a entity query and loop through the results.