If anyone's interested, here's what I learned today.
Met with the lawyer who supposedly "oversaw" my purchase of this property in the beginning, and he's pretty much washing his hands of the whole thing. He may be responsible for these problems, but for him to actually take responsibility, I would have to force the issue, which I don't have the time, money, or inclination to do as things stand now. He did give me a couple of names of other attorneys who might be willing to help if I can't get this resolved myself (what a guy, huh?).
As far as the status of those signatures I originally came here questioning, the lawyer says he doesn't like it and he would never do it that way himself, but he felt it was adequate at the time we made the purchase and therefore gave us the go ahead to close.
However, he said he could think of at least two attorneys off the top of his head who would never accept it like that and would insist on a correction being recorded. I think he should have rejected it way back when on that basis alone, but that's water under the bridge at this point.
If I were selling this house to a stranger, I would pray the buyer's title company would accept it the way it is, get my money, and do the "I'm-out-clean" happy dance. But my sister is the buyer, and if she tries to sell the house 10 years down the road and her buyer's attorney/title company won't accept it the way it is, it is very possible if not likely they would not be able to track all these people down. And if one of them were to die in the meantime, then it would be a matter of tracking down that person's heirs and convincing them to sign away an interest they never knew they had and who might decide to try to profit from it. This is just too fraught with potential future problems to lay at my own sister's feet. So I told her to contact her title company and make a stink about having it corrected. Even if it takes longer to close, she's not going anywhere as a buyer and she will sleep better at night for years to come knowing it is taken care of. I also told her she probably will want to get her own owner's policy and perhaps even her own attorney to go over everything before closing. Didn't work out for me like it should've, but all anyone can do is try to the best of their ability to protect themselves, and it probably would work out better for her. I had the unfortunate experience of getting involved in a deal involving three, count 'em THREE (at the minimum), incompetent disinterested attorneys, but they can't all be like that, can they? (Don't answer that)