On fighting on two fronts

So I frequently get in philosophical debates with my two most senior coworkers. It's a lot of fun, and we regularly touch those topics which aren't considered polite among friends--politics, religion, abortion, evolution, economics, etc. All that stuff people kill each other over in some other countries. But we have different opinions, viewpoints and degrees of tolerance, yet still end up having a healthy debate and exchange of information and ideas.

I've noticed that they each have very different styles of debate, if one defines a style as the types of arguments and counterarguments, approaches taken, sources of material, concepts and presuppositions, etc. One of them I can debate against quite effectively, usually breaking down the arguments and using them and their requisite assumptions in more effective counterarguments. I have a harder time debating the other coworker, but I can usually hold my own for quite a while. (I don't have a good metric for this; Debates get paused and resumed, multiplexed with other debates, etc.)

When I have a really hard time is when I'm on one side, of a debate, and they're both on the other side. (Actually, we each have a hard time in that position, and each such scenario happens occasionally.) I run into a problem where the the stipulations, assumptions and allowable assumed interpretations for when I'm debating one of them aren't all also valid for debates with the other, so I end up having to put in four times the work to try to make the same point. And making supporting arguments is even more difficult, because there are precious few complex and sophisticated stipulations that hold true for both of them, so I frequently wind up going deeper and deeper when making my supporting arguments, usually getting stuck somewhere in the realm of theoretical science.

"Theoretical science? You're not qualified to debate and discuss that. Why go there?"

Yes, theoretical science. No, I'm not qualified to go there. But I keep winding up there because I'm forced to back up assumptions about everyday phenomena with the underlying principles, and then have to back up the principles that underly those, and then...you see where this is going.

And as soon as we hit the level where popularly reported science hasn't figured out what's going on, then I'm stuck and have lost the debate about something that started as mundane as why people have babies, or how many generations back a family tree can go.

(Speaking of time, could someone please give me a rigorously proven way to explain the accuracy ranges of carbon dataing and dating by geological layers? Preferrably including an explanation as to the nature of the carbon 14 cycle, why we still have it if it's unstable, why we have any radioactive elements at all, and so on? It's one of those recurring foundation topics.)