Problem:

I want to use the view from the main site to the subdomains

Solution:

There isn't such kind of built-in feature, you might consider custom codes, for example:

https://toolset.com/forums/topic/multisite-with-toolset-2/#post-2318145

Relevant Documentation:

Problem:
How to display content from another plugin in views?

Solution:
Here is the doc how you can enable the third-party fields for view to display:
- https://toolset.com/course-lesson/using-third-party-hidden-fields/

And then you can use the [wpv-post-field] shortcode to display those fields:
For example:

[wpv-post-field name="_OrganizerEmail"]

Relevant Documentation:
=> https://toolset.com/documentation/programmer-reference/views/views-shortcodes/#vf-153444

Problem:

How to setup WordPress nav menus using Astra theme?

Solution:

The WordPress website menus are defined by your theme, since your are using Astra theme, you can follow their document to setup your website menu:

https://wpastra.com/docs-category/astra-pro-modules/nav-menu/

Relevant Documentation:

Problem:

Setup ancestor post type relationship filters with Blocks editor.

Solution:

You can follow our document to setup the filters.

Relevant Documentation:

https://toolset.com/course-lesson/creating-a-custom-search/