Project management: How not to lose friends and alienate people

I've been quite lucky in getting my grants funded. I've also been incredibly lucky with the team members I've managed to assemble. They get along with each other and I get along with them. They are my family. However, we have now reached a stage where I have to start making sure there is output. And if I am honest, I don't really know how to do that.

I have always worked for PIs who were very hands off. I have also always worked for PIs who were senior, male, tenured and financially secure. And while I was very happy to discover that I am not a natural micro-manager, I realise that I have to be way more on top of things than my own mentors have ever been with me. For them, it was okay if output came after 5 years. Or 6. In my case, I need output after a maximum of 4 or my contract will run out before my papers are in press. 

The thing is, I have some awesome people working on a very demanding project. And because I also have other obligations I just haven't been able to put any practical time in on it myself, although part of it really is my expertise. My peeps are doing the best they can, but there is just a lot more work than they can handle (plus the usual setbacks and sideways that need to be explored before we can pick things back up on the main road) and it is super clear to me that we need an extra pair of hands. I've got the funding to hire someone, but this is not going to be a 100% natural and organic merger. It needs active management from my side, because it is clear that my peeps see it as an intrusion on "their" project. They feel someone else may run off with "their" data. That he or she may interfere with "their" publications. And it doesn't matter how many times I turn "their" back into "our" in the conversations that we are having - they just don't see it that way. 

The thing is, I cannot blame them. I would have had exactly the same defensive response if it had been me as the person working on the project. And as they get defensive I become insecure as to how to handle this.

So.

I need help. 

How am I going to make sure that this is going to improve output from the project instead of destroying everything I've built so far? Of course I have everybody's best interest in mind, but guiding all of this into a situation where everybody gets the papers that he or she deserves requires leadership on my part that I am not sure I am comfortable displaying yet. 

I think we need to sit down together and divide work - but I've never done this: predicting who goes where on papers that are still completely up in the air and that may look entirely different tomorrow? It's basic science. Who knows what we will find. And even if that's the way to go - how do I get them on my side, not just logically but also psychologically? I know they will probably see (once everything is sketched out) that there is too much work to do for just the folks we have now, but that doesn't mean they will just welcome another wheel on the wagon. They are working hard, they are tired. I want to treat them as equals. But in the end, I am in charge. They don't need a friend right now, they need a boss. And I need to figure out how to do that.