Ask HN: How do you manage projects in adversarial circumstances?

Hey everyone, I've been put in charge to manage a 6-months long project that involves many senior stakeholders and many impacted development teams (i.e., they will have to add new items to their backlogs). Now, I realize that (1) the senior stakeholders have conflicting priorities at their org level (siloed, protecting their roadmaps and capacity), which also seems to trickle down to the working level with all the development teams. In addition, this is also work on top of their regular roadmaps, and there is not really an adequate capacity planning done for this additional effort.

Now, it seems far from the "happy path", but how I do I try to turn this around? What are ways I can still motivate all the impacted parties to take on ownership for the project, bottoms-up?

Any references to research/academia/case studies would be highly appreciated.

Thank you!