Well, we had The Conversation. It actually went better than I thought. It turns out that Laura felt that it wasn't working either and was planning to have the same conversation with Jane and me, so the hard bit (as in, not doing the business deal) actually went very smoothly. Unfortunately Laura and Jane have some issues in their friendship (unrelated to our business, Jane and Laura are long-standing friends of over a decade), which they are going to discuss separately. However, my reading of the situation is that they'll work it out when everyone calms down a bit...I hope.
It's not 100% over yet though, as Laura's more hurt about us wanting to move to a new premises. She really doesn't want us to move out, so much so that she offered to move Carrie out of "our room" so that Jane and I could have it to ourselves...rent free. (Personally, I like sharing the room with Carrie, she's great.) I'm wary of going that route, though the boundaries could possibly shifted in mine and Jane's favor as we'd no longer be financially tied Laura; her offer is very kind but I think if we did stay in the office we'd have to pay rent just to make it clear that we are tenants, not someone for whom Laura's doing a favor. Plus we'd actually be able to close the door and truly have our own space. However...
One of the big suggestions on that thread was for the three of you to sit down and discuss boundaries and how you expect to be treated. Did you do that? How did it turn out? Did she agree and then just not follow-through?
...we did have that conversation, and Laura agreed and apologized. I admit that her demanour around Jane and me has been better, but she's quite awful to some of her own employees and it makes for a very tense atmosphere. For this reason Jane is not keen on staying in the building at all.
Incidentally, I went out with Laura last night; I thought it was important to not avoid her and reinforce the fact that I want to continue the friendship. I think it was the right thing to do, as we had a fantastic time. I eventually will broach the subject about the bullying. I think it will be easier to do as a friend giving advice, instead of as a business colleague pointing out mistakes.
Anyway, I wanted to say thanks again for everyone's support and great advice. It was a big help in a very awkward situation.