Are there any home care providers in SoCal who are affordable to a couple on SS? Dad's dementia is getting worse & mom can't handle it.

The reverse mortgage on the home may hurt their ability to seek medicaid for placement of Dad, and clearly, at 88, they are too old to handle Dad at home. The drug addicted daughter at home is an exceptionally unwise decision, whoever made it. She may need to be evicted. Instead your mother is supporting her with her money.
Dementia drugs don't cure. None are proven to cure as yet. So the fact that Dad isn't on drugs is neither here nor there.
I would suggest placement for both your Mom and Dad, sale of the home at once (paying back the reverse mortgage and spending down what is left of the rest of the money in ALF, then moving to medicaid for their care. They are both too elderly for there not to eventually come to disaster. That is to say, this is self-limiting, this situation. At some point your Mom will crumble after this, and that will leave your coming to take care of things.
Are you the POA? Has anything at all been done to address what is inevitably coming?
As to inhome care, I can't know how much money is incoming on reverse mortgage, but it should be going to care rather than to the addict daughter who is being enabled by it.
You have a very complex situation. At some point you will be left with reporting this to APS for in home assessment.
Sorry, I sure hope others have some better ideas for you. I can find no hope in this situation. It seems to me so desperate for so many reasons.

I 100% agree with JoAnn29 to help your mom get him placed and apply for MediCal -- hopefully having a reverse mortgage and supporting loser sister won't disqualify them. Do you think your mom, at 88, will be able to manage this on her own (assuming drug addict sibling is no help)? I would strongly recommend you take some time off and go help her if at all possible (even a week would be better than nothing and maybe you can extricate the loser sibling as well).

FYI dementia medications need to happen early on in the disease and often don't do much except *maybe* slow the progress. If your dad is having bladder incontinence it could also be from a UTI. It will be much easier to help in person, if at all possible. I wish you success in this situation.

You start with MediCal. I would suggest that Dad be placed in a Longterm care facility. MediCal, if like Medicaid in my State may not give him 24/7 care. And you deal with people who have lives that may not show up or on time. With LTC you know someone is always there. Mom will becom a Community Spouse receiving enough money to live on. She will be able to remain
in the home.