I am setting up a magento multistore.

I want to have one main child theme with layout and css changes, that every site should have.

From this theme my site-specific child themes should inherit.

I have already set up successfully simple child themes but the above constellation does not work. The changes from "main child theme" are not visible.

Can anybody tell me if this is possible?

Main-Child inherits from Luma
Site1-Child inherits from Main-Child