Relationship between taxonomy and categories in WordPress?

Question

Taxonomy

I have a question!
There are Posts - these are our products!
There are Rubrics/Categories - these are our product categories.
There are Taxonomy of brands (brands) - where restaurants are stored!
Both the product category and the brand taxonomy are assigned to the post.
What I need is, when the user is in the taxonomy template, the products related to the taxonomy (brands) are displayed there, I need to load the product categories into this template, but the product categories need to display those that relate to the products displayed in the current brand!
Guys, please help who than you can! If possible, write an example of a function how to implement it and how to load products from the list of categories on the taxonomy page in the future! Implementation on post, get, ajax, etc. no difference!