Since you haven't mentioned the actual dollar amounts, this may be way off base. I also admit that there are multiple ways to accomplish some of these goals.
That said, whenever someone needs to be protected from themselves (too much spending) or from a mooching relative, a large portion allocated to an immediate annuity might be in order. A life and thirty year certain would give granny a guaranteed stipend for as long as she's alive. The monthly payment could be deposited into her bank account, and that's all she has available to 'help' anyone that comes around. The immediate annuity would continue to pay to a beneficiary if she dies in first 30 years. At age 78, you're likely looking at a 4-5% payout annually. You could back load the payments with a 5% inflation adjustment, meaning less paid out now (you said her expenses are currently covered) and more paid out to beneficiaries. Speak with your elder law attorney, but making this type of annuity irrevocable should also help with LTC planning.
I would not advocate putting everything into an immediate annuity, perhaps 75% max.
Another option might be a CRAT/CRUT. Give the money away now to a charitable foundation, collect payments for life, designated charity receives corpus at granny's death.
IF you really want to piss off the rest of the family (or don't care that they are pissed) have granny underwritten for a life insurance policy now while she is healthy, and have your wife be the owner and beneficiary. You have already set the expectation that your wife will be a caregiver at some point--likely uncompensated--this would be the de facto LTC plan that would compensate your wife in arrears for the care she provides. The life cash value would be out of granny's name/estate, but still be available to your wife should she need/want access to it while granny is alive. Granny would gift the premiums to your wife from the proceeds of the immediate annuity or CRAT. Medicaid and mooching family members would have no leg to stand on.
Flame away...
Ridin' 'cross the desert. . .