Replication with transformation, how difficult?

Question

Oracle

Task:
Oracle DBMS has two schemes running on the same instance (RAC) - OLD_DB and NEW_DB, it is required to build one-way replication from OLD_DB to NEW_DB, for a long migration ~ 2-3 months.
The replica can be realtime or with a delay of 1-2 minutes.
There are ~100 tables, most of them repeat each other, only with the replacement of names or individual columns, and about 6 tables for which a serious transformation is needed, splitting one table into two (always or by value one field) and vice versa merging 2 tables into one.
Are there ready-made tools for such a task (of course, mapping will have to be done by yourself) and how difficult is this task in general?

Thank you in advance.