I am a postdoc with a double affiliation (I belong to two groups in different departments but same institution). As such, I work under main supervisor A and under secondary supervisor B, meaning that most of my funding comes from A, who also is officially appointed as my superior. I work mostly on common projects between A and B, but also on A's and B's independent projects, and some of my own stuff.
I am currently working towards further independence, which is in principle the purpose of a postdoc. This involves participating in grant writing and decision making, for example choosing which conferences to go, journals to publish, more flexibility in the approach to problem solving, etc.
Recently, I got funding to hire two people from a successful grant I wrote with A. I was responsible for designing most of the scientific part, as well as risk management, scheduling, etc. Because of my involvement in the project preparation, A wants me to also be involved in interviewing and selecting applicants. We also decided that the most convenient way to articulate these positions (in terms of accessing resources) is for them to be in a double-affiliation scheme between A's and B's group, just as me. Obviously, B agreed to this since they benefit from two new appointments at no (money) cost to them. And obviously B was also invited to participate in the interviews and selection process.
Already after the applicant selection has started, B seems to be making somewhat erratic applicant assessments which go against mine and A's judgement. We thought this was very strange because their assessments did not appear to make much sense to us, until B eventually openly added that my opinion should not be taken into account. At this point the whole story put together seems to point to the direction that B basically wants to undermine my input in the decision making process.
This is not an isolated incident. B has also been increasing the control that they exert over my work. I get the feeling that B somehow feels threatened by my increasing scientific independence and somehow wants to let me know "what is my place". Incidentally, and probably adding to the problem, B is not much more senior than me and is trying to establish their research group.
How can I defuse this situation such that I do not burn bridges with B: a bad relation with B could hurt my chances to progress in B's department. At the same time, I want to progress in my independence, and this obviously involves being part of personnel selection and project design.