DLL for ORACLE-Access

I need a dll to work with Metarader4 (mql4) an ORACLE XE databases:

- no Java or something like that, it should be fast and safe

- no ORACLE-client installation on the Client-PC

- SELECT (single- AND multi-row), INSERT, UPDATE, DELETE, and any other ORACLE-SQL-Statement should work

- commit, rollback 

- no need of  DDL, only DML

- 32bit AND 64bit Operating Systems (Minimum Windows in all versions)

- we want to have all rights to the source-code (and the source-code of course :-) )

- before, we'll discuss about the way of implementing and the used techniques

Any ideas? :-) 

Let me be a little bit more precisely:
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- We're writing EAs with MT4
- I want to connect EAs (written in MT4, build>600) with remotely installed ORACLE-databases (more precisely: the EA runs on the computers of our clients, the database runs on our PC)
- There must be no installation of ORACLE-client on client PCs (so: What technique will you use? OCI?)
- The only installation on the client PCs should be your dll
- No further installation on the database PC except the ORACLE database (of course with the ORACLE-client)
- We need the following functions:
  => No limitation (except the ORACLE limits) to the length of the statements!
  o connecting (and reconnecting) to a database
  o disconnecting a database
  o rollback
  o commit
  o select (single-row)
  o select (multi-row)
  o DML (update, insert, delete)
  o multi-session (1 session in 1 EA-instance, but a lot of Ea-instances at the same time on different client PCs)
  o transactional
- Every function must return the ORACLE-error-code which has been returned from the ORACLE-DB when running the ORACLE statement
- The DLL must work with Windows 32Bit AND with Windows 64Bit
- used Windows Versions: (maybe Vista; not really important), 7, 8, 8.1, 10 (in every release, f.e. Home, Pro, ...)
- we need all rights to the dll, and the source-code
- inline documentation (every instruction/command) in English or German
- good outline documentation  in English or German
  o explanation of every function, every parameter, return value
    => I think, in most cases, 1 or 2 Sentences are enough :-)
  o installation guide, using guide
    => how to use and how to handle with the dll, some little examples, etc.
  o dll creation guide
    => in order to make changes on our own after you finished your job
 
Questions:
- Which tool (f.e. MS Visual Studio for C++, pro*c, etc.) will you use to create the dll?
- Which technique will you use?
- What are the limitations and/or the requirements?
- How long does it take?
- How will you connect to the database? Which connect-string or which connect-method?