Situation normal all fouled up

So I am stuck in a German catch-22. Maybe. Can anyone help me out here? By now I know German pretty well, even by my standards, and I can talk my way through almost any given situation (if not flawlessly). But one thing baffles me still: du or Sie? German, like Spanish and Shakespearean English and lots of other langauges, doesn't have just one way to acknowledge someone in the second person. Nope, you have to first split the world up into people-with-whom-I-have-an-informal-relationship and people-with-whom-I-have-a-formal-relationship. Friends, parents, young children and God fall into the first category; teachers, customers and strangers fall into the second. OK, so far so good. And if all else fails, mimic: they say Sie to me, I say Sie back, and likewise with du.

But there are some areas of gray. For example, if a teacher says du to you, you aren't automatically allowed to say du back to them. It's a respect issue. And then there's your friends' parents. (Or, even more agonizing, boyfriend's parents.) When do you stop being a stranger and start being a du-able part of the family? I have had conversations that sounded utterly contradictory to my ears--a heartfelt invitation to visit again whenever I wanted, coupled with the declaration that I had "won a place in their hearts," but juxtaposed with this cold, jarring Sie. Sie does not say to me "you are dear to my heart." Sie says to me "would you like fries with that?" or "So how long have you have this supporating wound?"

I get the feeling it's sometimes not altogether clear to Germans either. There was a professor's assistant with whom I had a pretty friendly relationship. I think. We hung out together in an Italian monastery for a week, then I took a couple of classes with him, translated a big project of his, etc. Nice guy. (It's not like that! He was gay!) Now, you always "sietz" (that's the verb) professors in Germany. But assistant profs are another matter, and after we knew each other relatively well he started to "dutz" me... most of the time. And so I was thinking, OK, then I should dutz back, right? Because if they think you are at a dutzing stage, and you still sietz them, then that could be insulting. Like giving someone a linguistic cold shoulder. And so I avoided personal pronouns altogether for a while, during which time I had almost reached the conclusion that yes indeed, I could dutz him to my heart's content. But then a Sie would slip back in there every once in a while and I would get all hesitant again and go back to my rhetorical questions and slightly strained overuse of the first and third persons.

It must be confusing even for Germans, trying to remember who is in which category all the time. Maybe that is one reason for the emphasis on structure and hierarchy.

Anyway, that brings me to the question at hand: as you know, there are two new employees in my building, who seem at least nice enough to add to my scanty list of friendly acquaintances in Wittenberg. So far we have exchanged only formal self-introductions in a big circle and a little idle chit-chat. I'd like to invite them both over to dinner or something ("like" being a mild term for my insanely passionate desire to know more people here), but I don't know if I should sietz them or dutz them, and I can't think of a way to phrase an invitation without having to say "you" at some point. I would guess from their background and education that we are about the same age, within three years or so anyway. But maybe the "colleagues" rule trumps the "potential friends" rule. I don't want to offend by affecting a distance that's not there; I don't want to offend by creating a false intimacy either.

I don't get it. It is one of those cultural sensitivities that you can't really learn on TV. All I get from German and dubbed TV is that after you kiss and/or have mad passionate sex, you are definitely "per du." That made-for-TV rule does not really apply in this situation, however.

If I had my way, I'd du-tz the whole world and be done with it, but that's my crazy informal US-American mind for ya.

Hmm... I gotta go, my evening entertainment calls. Wedding Planner, here I come.