Q1, Export using statement OWNER=(user1), then import using statement FROMUSER=(user1) and statement TOUSER=(user2).
Q2, No need to give authority, as the user1.table1 will become user2.table1.
Q3, If OWNER has given grants to their tables, views, etc. then TOUSER would need to do the same if required. Example if user3 has access to user1.table1, they’ll lose it once the OWNER schema is dropped.