Tough stuff Michael. It's good you're trying to help your mom, but remember that her connection to your grandparents is different than yours. The emotional part of it. That's her mother and her father, not yours. She's not going to have the same sort of ability to 'detach' herself and see what you consider to be better options.
Some countries have no social services whatsoever. It's just understood that family takes care of family, no matter how much they want to murder each other.
I've been a caregiver before. It's very difficult at times, extremely stressful and sometimes infuriating. But I wouldn't have done any differently. No way did I want 'strangers' involved. And that stubborness has a price too 
These days there are HHA's and CNA's and sometimes they work as, essentially, contractors and sometimes as part of agencies. These folks generally require insurance. In rural areas though, you can advertise for help and pay someone a certain amount to come spend *some* time during the week with them. The point for you seems more to make sure your mom gets a break from what can often feel overwhelming. And that's a very good idea.
Since your grans have a lot of pride, you could figure out ways to spare them any perceived 'insult' by introducing these people as friends or something. Those who work with the elderly often know how to 'get in' with them, get on their good side so to speak. I say let them do any little things they CAN do and continue to circumvent them on things they can't. You just can't let them know it's happening LOL Are there any other relatives that would be willing to spend a day with them so your mom can get a break?
Some states have good social services, others do not. The one I was in did not. Right now, so many states are in financial meltdown that there's just no money to go around for these things. People haven't quite got their minds wrapped around that yet, but they will...
Old people are going to do old people things. Mental sharpness goes downhill fast, cognition burps, a little paranoia surfaces, the body starts to fail. I'm sorry for being so direct but I've been in a similar situation and sugar coating things, IMHO, doesn't really help. I do hope that you all can find some assistance in *any* way possible.
I've a friend here who isn't technically trained, except in CPR, as a CNA or HHA but she does have a couple of old people she tends to during the week as her job. This is a rural area as well. Some people are looking to make some money here and there so if any of you have a spare $20 during any given week, you can maybe make contact with someone who could give a couple of hours to helping out at a day and time you need them most.
I feel for your mom and it sounds like she's just trying to do what she thinks is right and what she should do. And, as Tito and Dandelion have more gently put it, the price of getting in the ring is sometimes you get hit But, it takes a lot more strength to get in the ring than to sit and watch, doesn't it?
but it's great that you visiting helps... maybe it also helps just to be able to talk about other things with company, yknow?
funny how that happens. (not funny "haha"... funny crummy.)
