Run stored procedures in other schemas from stored procedure
You can call procedures in schema B from procedures in schema A. Depending on the version of Oracle, you may have to grant execute privileges on each procedure explicitly from B to A, using the "with grant" option, rather than through a role. Consult documentation for your specific version to verify what permissions are required. 

In general I would also recommend putting orchestration logic into the back-end (database) rather than client-side code. Keep your back-end and front-end business logic separate.