How to work with a RA unwilling to work with me? I've recently started a new role on a three year project. I'm a research officer and I've joined onto the project about 8 months in at new research institute, there are three CIs. I've been brought on due to my expertise in a set of areas that the project is lacking, which includes theoretical/methodological knowledge and project management experience/skills. In terms of hierarchy, it's the three CIs, then me, then the RA. I've been brought on as a new early career researcher having already completely my Phd. 

There is a graduate student research assistant involved with the project and their contract will finish at the end of the year. There is no money for additional work for them, and it is expected that I'll be taking over all of the their duties in addition to project management as well as creative contribution. The RA has been tasked to support me in the transition period as I take over the project and see out its implementation. 

I've been getting along well with the chief investigators and am beginning to settle into the role. However, my struggle is with the RA, who is unwilling to work with me or allow me access to any of the materials. If I ask them to help me with something, they go to one of the CIs and complain that they are confused about what they are being tasked with. In meetings, I find that they roll their eyes at me, and give off a hostile vibe. In some cases, I feel as though my intelligence is being belittled despite being brought on as a senior researcher, because my research background, (while complimentary) is quite different to the standard background at this institute.   

I know that this could potentially be a bit of backlash for me being brought onto the project, and that they are concerned about their contributions. They have been told that they are not staying on past a particular date (or so I've been told), and there might be some unintentional gate-keeping/attachment to the project that they are unwilling to let go. However, they've also been made aware that their contributions will count towards co-authoring a paper or two, so they won't be kicked off completely with nothing to show for it. 

While I have brought up this issue with the CIs, it's still happening, and I'm not sure what the next step is or how to manage this effectively.

Has anyone had this experience before and can offer some suggestions/guidance?
Have an honest conversation with RA, bring the CI and perhaps have a group meeting. Be straightforward. If there is just one thing I learned in my years of not only academics, but life, it is to be truthful and straightforward. Although it may come across as harsh, it needs to be done.