Based on an IDIQ in place is contracting able to support a new requirement that will result in two contractors supporting the same requirement?
Contracting officers can make multiple awards of IDIQs under a single solicitation for the same or similar services to two or more sources, but the terms and conditions of that solicitation must clearly state multiple awards will be made. It would appear the current requirement is a single-award requirement and most likely would have been solicited as such. If two or more contractors are to perform, then this would require following the requirements of multiple-award contracts in FAR part 16, take note of when multiple awards are not to be used in 16.504(c)(1)(ii)(B), which may apply to your situation. In the cases of placing orders under multiple-award contracts, the rule of fair opportunity at FAR 16.505(b) will apply.
Is there a bona fide need for two separate contractors to be performing the same service? The below link is the 2021 Fiscal Law Deskbook that is an excellent resource for fiscal law matters. While this resource is issued by the Army's Judge Advocate General's Legal Center and School, it contains information that is helpful to all DoD personnel. In the section on limitations on the use of appropriated funds starting on page 1-6, the Deskbook addresses the three aspects of the bona fide rule, which are purpose, time and amount. This question would require coordination with your local staff judge advocate.