My husband lives with his elderly parents: father has arthritis, heart disease, and other issues but not dementia; mother is in late stages of Alzheimer's disease. Lately, during our infrequent conversations (my husband rarely initiates or responds to communications), my husband has described to me his mother's recent sharp decline. He has not taken her to the doctor. He has not called the doctor. He has not talked to his siblings. He and his father are doing everything on their own. From what my husband has said, I think my mother-in-law might be actively dying and I think the siblings should be told so that they can decide what, if anything, to do: visit; call; pray; whatever. I'd appreciate any thoughts about what, if anything, I should do. Thank you.
To make any progress, your husband will need to leave his parents before any therapy plus meds would be effective, but even then it does not sound likely like he would go. Maybe, he will leave after your MIL passes.
Are there any of siblings that you feel close enough to call on the phone and talk about what is going on? I can't think of any other way to have someone from the outside to intervene in this crisis.