If we have subcomponents inside a multiple field, we need to create a component container with an empty cq: design_dialog (this allows to be a child element, otherwise the component will be a child at the root and not in the parent) and an html file to display the component.
This is the example to solve my problem.
Primary component: call to title and child container component
<div data-sly-use.placeholderTemplate="core/wcm/components/commons/v1/templates.html">
${properties}
<div data-sly-resource="${'title' @ resourceType='wknd/components/content/title'}">
</div>
<div data-sly-resource="${'internTitles' @ resourceType='wknd/components/content/nidhiMulti'}">
</div>
</div>
container child: it is call two components for finally show the title component
<div data-sly-use.placeholderTemplate="core/wcm/components/commons/v1/templates.html">
<div data-sly-resource="${'item0' @ resourceType='wknd/components/content/nidhiTest'}">
</div>
<div data-sly-resource="${'item1' @ resourceType='wknd/components/content/nidhiTest'}">
</div>
</div>
last subcomponent:
<div data-sly-use.placeholderTemplate="core/wcm/components/commons/v1/templates.html">
<div data-sly-resource="${'title' @ resourceType='wknd/components/content/title'}">
</div>
</div>
This allows you to have a component with a multi-level hierarchy in the content tree.
It is the solution found by me, it may be simpler but it is just an example for more complex cases. if someone has a better method, please, I hope to read it. Thank you.