Connecting two custom entities

Hi,

I have three custom entities (A, B, C) which are related so that B and C are related (1:N) to A. (So there is currently no direct relation between B and C.) Now I want to create a word template from entity C, but using data in a sub-grid in entity B. How do I do it?

Thanks a lot for all help and ideas.

Regards,

Mia