The Editable image web part is not designed to be used inside another web part. You can separate the web parts; use the original Editable image web part and the rest of code in a custom web part.
If you need to use the Editable image inside your custom web part, the parent web part must:
inherit from the CMSAbstractEditableWebPart class and
implement the LoadContent and GetContent methods.
You can take inspiration from the Editable image web part: