The "tables of the relationship between two other tables" is a Many-To-Many Relationship. This can be achieved by giving both tables an ICollection List of both Classes. EF Core will do the rest and generate it.

https://learn.microsoft.com/en-us/ef/core/modeling/relationships/many-to-many more on this under the chapter Basic many-to-many

Now to your disliking of storing an entire model of the DB in code. Why exactly don't you want to do it? Is there any specific reason?