Dementia Support Group
Dementia is the progressive decline in cognitive function due to damage or disease in the brain beyond what might be expected from normal aging. Particularly affected areas may be memory, attention, language and problem solving, although particularly in the later stages of the condition, affected persons may be disoriented in time, place and person (not knowing who they...
I would say to try to get some help in the house, especially to give your dad a break. That way you can devote time to your son and away from grandma for a certain period each day. And your dad sounds like he needs a break. One day your mom may hav eto be cared for by someone else, and it is good if she can get used to it now.
Caregiving can be creeping - one day you look up and it has taken over your life and you and your life are a wreck. It sounds like you are nearing the tipping point.
Also call the Alzheimer's Association and let them get you some resource material.
And from the sounds of it, your Mother is in Stage 7 which means that in the US, Hospice would be appropriate. Ask her doctor for a referral so she can be assessed.