Use Parent and Child theme together in a multisite

Hi,

Following constellation:
In a multisite with subdirectories:
– Blog 1 uses parent Enfold
– Blog 2 is supposed to use child Enfold.

Blog 1 (Parent) has customizations in its custom.css.

Blog 2 (Child) should use the customizations in the parent’s (!!!) custom.ss and yet in child theme/blog some of these styles are to be changed only for the child from case to case.

Do the styles of the custom.css of Parent Themes (Blog 1) inherit on a Child Theme in Blog 2 (Multisite!)?

Note:
Copying the parent’s custom.css into child’s style.css is not an option, because the child should use the styles in the parent’s custom.css whenevers they change, so to say “dynamically”

How can I achieve this please?
Thanks.