Looking at your requirements, why don't you just create a different schema as pando suggested, or create a set of roles with the access privileges and grant those roles based upon the user requirements.

project-A.schema
project-B.schema
project-AB.schema

Create roles with insert update delete

role_IUD-AB

Grant role_IUD-AB to project-A
Grant role_IUD-AB to project-B

Now go ahead and set up the table level triggers with AFTER insert,update, delete and fire them on the project-A.schema,project-B.schema to make the changes in the project-AB.schema

Now you can give full/select privileges to the person who ever want to use this AB schema to view objects.

But remember here you would be maintaining two sets of redundant information.

-Sam