I've been reading along and honestly, I'm rather confused. Some of your posts just sound like different stories from different people. I could be totally misreading but some of this sounds a bit contradictory. I'm still confused as to what it is exactly that you're worried about your husband even doing. I know that this format is difficult to convey complex situations and emotions in. On one hand you seem to be saying that you need strict boundaries to make sure no one messes up or gets too attached but then you say that the relationship is free to develop emotionally. I hope you can see how some of your statements might seem a tad contradictory. All we have to go on is what you give us. In your last post, you say you have a powerful, workable dynamic. But some how this whole situation comes off sounding like you're all dancing on the edge of a knife hoping not to fall to ruin.
I guess I just don't know a) what the problem is precisely, b) what everyone's responsibilities and roles are and c) the expectations for the future/possibilities for boundary renegotiation
Obviously, I agree that your husband should not be trying to 'renegotiate' boundaries during sex. Still, I feel confused about what it is you're asking.