Jen,
This is a sore subject with me because my situation is similar. I have soooo much to say that's it's hard to know where to begin without being all over the place and still be helpful to you. I take care of my 88-year-old maternal grandmother while fulfilling the responsibilities of being a wife and mother of three young kids ages 4-7. My grandmother raised me, put me through private school, bought my first car, and on and on so I have the same burden in my heart for my grandmother as you do for yours. My mother, who was her daughter, is dead and her son is nowhere to be found so there is no one but me.
Here's where you have an advantage: you have people who can and should be taking care of your grandma, but they won't. I know you say they have a lot going on in their lives, but the difference between you and them is that you've made adjustments to care for grandma despite what you have going on--for everyone else that has been an option.
The first thing I had to come to terms with and that I think you need to accept is that someone has to make the difficult decisions and/or be the bad guy and that somebody is you. There is no easy way to deal with this situation. It won't be pretty. As a matter of fact, wear the bad guy badge with honor because until you start the ball rolling, the things that really need to get done for your grandmother and the decisions that really need to made on her behalf will never be accomplished if everybody just lets things continue on the way they have been.
Once you come to terms with that then you need to move forward. I would start by having a "Come to Jesus" meeting with the family. Emphatically let them know that you can't do it anymore. Be strong and be courageous. Don't let them turn it into an apple and oranges debate where they go back and forth with all the reasons they can't take grandma. You didn't call the meeting for that and frankly that's not your concern at this point. All they need to know is that you can't do it anymore. As far as I'm concerned, they don't even need to know why (that your husband is burned out), that's not their business. And most importantly, DO NOT APOLOGIZE. You have been nothing but a blessing to your grandma and you aren't letting her down. Be strong and shut down all attempts to make you feel guilty.
If your family won't take your grandmother willingly, then start a legal chain of events going. WITHOUT paying a lawyer, I filed petitions to the probate court to become my grandmother's guardian and conservator and was granted both. If your aunt and uncle won't take your grandmother willing after you tell them that you are done, and you said that legally your mother can't be her caregiver, then I agree with a previous poster here that you need to file a petition for her to be a ward of the court and have the state of Utah declare her a protected individual so that her assets can be sold and the proceeds used toward her care and/or she can receive Medicaid and be placed in nursing home (it sounds like your grandmother's dementia has progressed to the point of needing placement in a facility especially combined with the physical ailments that you mentioned). If you can include doctor's assessments with your petition, then good. If not, then the state will have someone evaluate her. It will start with a court representative (the guardian ad litem) and then his or her report will call for a medical evaluation. Do know that you aunt, uncle, and maybe even your mother will be livid as they will be notified by the court of your petition because they are considered interested persons and will be called to show up at a hearing. They may even contest, which would be good on your part because if they contest, then all the court will want to know is which one of them will be taking your grandmother since they are contesting. See this is the part that has been optional to them previously--their involvement-- they do when they feel like it, but when it is too stressful and/or grandma gets to acting up/out then "they have their own lives". What you want to do is create a situation, one way or the other, that let's them know that their full-time involvement with your grandmother is NO LONGER OPTIONAL. As a previous poster commented, it's funny how they're still all up in the financial parts of the matter--They don't want you to have grandma's house, but they don't want to take care of her fulltime either--time out for that nonsense. Again, remove the options. The reason I'm not suggesting that you become your grandmother's guardian and conservator, or even become her caregiver for compensation as was suggested by another poster, is because you've reached a point in your marriage where you have to let go of the responsibility of taking care of your grandmother.
Speaking of your marriage , the paranoia, the accusations, the depression, the downright orneriness from your grandmother--I'm right where you are. So far I am "managing" my grandmother (I laughed as I typed that--some days are better than others) and my husband knew the first week that I met him that my grandmother was a huge part of my life. She was the first thing I told him about, just like the first thing a single parent mentions to a first date is her children. (although my grandmother didn't have dementia when we first met and got married and we like you and your husband lived with her for a short while during our marriage) However I do have a limit, and that limit is losing my husband. Consider that limit for yourself. My husband has been tremendous, but if/when he approaches me and says that he can't do it anymore, I know that he has already gone to the wall for my grandmother and has given and done more than any of her blood relatives combined (I suspect the same can be said for your husband) and enough is enough. I've already accepted that even if he doesn't, her dementia will progress to unmanageable point anyway and she will have to go to a home. It sounds like the time has come sooner for your grandmother.
As for you and your family's promises to your grandmother that you wouldn't put her in a facility, you've got to ask yourself (and your family members at the Come to Jesus meeting), "is that realistic?" Your grandmother's condition is just too big for you now and yes you do owe your grandmother. But what you owe her is to do what is best for her, not to refrain from putting her in home where a team of people care for her 24/7. Especially if: a) the other family members can't seem to make her a priority and b) she's just too far gone now. If you've gotta tell her she needs to be in home so that they can treat the cancer she thinks she has then so be it--do what you have to do. Putting her in a home is not easy, but it isn't a crime. I'm not even suggesting that a caregiver come to your home because again, I believe the situation has reached the point where your grandmother needs to leave your home. If money is a concern, then check out the best homes that will accept her medicare with her social security paying the balance or copay or that will accept medicaid if you can get her on it (if you can get the state involved and get a case worker, that should get her moved closer to the top of the list for aid and placement). I know those facilities aren't the most upscale (something that I've had to come to terms with because money is an issue with me) but again we've gotta do what we gotta do. It doesn't have to be your marriage or your grandmother. Having a family or your grandmother. You've just got to make some difficult choices about what to do for grandma. And thus far you have been operating (and your family has been making you feel) like you don't have a choice, but you do--it's just hard. Guess what, everyday, and I do mean everyday my grandmother insists on going back to her home (she keeps her bag pack and declares she's going to the airport). She doesn't agree or understand why the court is involved. I don't say a word because I know it's not her choice to make anymore (and she can't process it anyway). The decision making is mine now and it's tough, but I have taken control. I'm urging you to take control.
Lastly, and I hope this doesn't send up a red flag with Caring.com or offend you, but get to know God. If you already know him then really get to know him.
Hold your head up high. Writing this note has been therapeutic for me and I hope it has been encouraging to you.
KC