Okay I have been working on this for a few days, and I don't have ALL of the answers, but this is what I have thus far:
Todd and Willow are living in Palmer, and Willow is attending classes there.
Sarah and Piper are in an undisclosed location together. (Your guess is as good as mine at this point.)
Bristol was spotted at the Palmer fair with two babies (multiple sources for this) but nobody seems to know just WHERE she is living.
What is fairly clear is that Sarah and Todd are not together at this moment and that Piper is not going to school in Alaska. (Not exactly a big surprise.)(Update: Uh oh, not so fast. Now there is information coming in that Piper may in fact be attending school in the Valley as well. Like I said, I don't have all of the answers yet.)
From what I can gather Bristol has been left in charge of the two babies, though I would assume she is getting some help. Perhaps from her grandparents or other family members. But that is pure conjecture on my part.
I may have some more information after this weekend but I cannot promise any new revelations.