BEB,
If I understand your question correctly, you are asking what is required to be a CPL instructor and also an Instrument Rating Instructor.
OK, First for the CPL you need a miniumum of 500 hours including 200 hours as an instructor, plus a full CPL (or ATPL), unrestricted FI rating and the required class/type on your licence. For you to be able to train CPL students, your FTO will conduct in house training, but there is no external test to pass only the in house requirements. Obviously, these will vary from school to school.
If you already hold an FI and wish to teach students to IR level, you must first hold an IR and have the applied instrument restriction removed. This is done by any FIE or Staff FE. To teach the IR you must also have logged 200 hours flight time in accordance with IFR (up to 50 in the sim). You can claim 4 hours IFR for every 1 hour flown by sole reference to instruments and not under IFR.
Of course, if you wish to teach IR ratings then chances are you will also need to single pilot multi engine privileges added to you FI rating. That is another kettle of fish.
The IRI is a standalong rating for people wishing to teach for the IR, but have no previous instructional experience and hence would not apply in your case. FYI, it required a valid IR, 800 hours logged IFR, pass a groundschool and a flight test.