^I am getting amazing advice -- more than I expected, and a lot to bring to my mom and sisters. Thank you everyone!
I do have power of attorney, fortunately, we signed all those papers over the holidays. I also have direct control of about half of her finances. One of the ways she's tried to make up for my mother's childhood is by helping to support her now. My mom can't work because of her disabilities, but my grandmother bought her a house last year, and gives her an allowance which will be continued in a living trust. Right now I have power over that half of the finances, but my grandmother's businesses and investments are all over the place and I have no experience in these areas at all.
She doesn't have any friends in homes that I know of, but she is very close to her brother and sister, and they actually all live next door to each other now. For awhile her brother and his wife were considering moving to a senior community, which would have made this so much easier because she would have happily followed them. They decided against it, though, and to make things worse, her sister's son moved in with her sister and brother-in-law to take care of them, which will make my grandmother want to stay where she is. I just don't see how that's feasible, though. Right now she's living in an apartment in a boarding house she runs, and the residents routinely take advantage of her (she's a horrible judge of character), and she's just not capable of getting by on her own any more.
Unfortunately, I can't fly out to Seattle to deal with this stuff, because I work...so, again, the remote management is hard.