SQL Server 2012 :: Select Maximum - Using Fields From 2 Tables?

I have Database Library, which has a lot of tables and we need 3 tables for quary:

Table Librarians: field ID, field Surname;
Table StudentCard: field ID, foreign key on table Librarians and other fields, which we don't use
Table TeacherCard: field ID, foreign key on table Librarians and other fields, which we don't use

Query: Select the librarian's surname, which gave the most count of books.

I know, how to resolve, when i took datas only from one table, e. g. TeacherCard

SELECT TOP 1 WITH TIES Librarians.LastName, MAX(Librarians.CountOfBooks) AS Books FROM
(SELECT L.LastName, COUNT(*) AS CountOfBooks FROM Libs L, T_Cards T
WHERE T.Id_Lib IN (SELECT L.Id)
GROUP BY L.LastName) AS Librarians
GROUP BY Librarians.LastName
ORDER BY MAX(Librarians.CountOfBooks) DESC
GO

I dont know, how to use datas from TeacherCard and from StudetnCard at the same time.