We're a family of three, my mom, my dad and I. My dad's father has recently been diagnosed with stage 4 cancer and, based on what we know so far, there's no chance for a recovery and not much life is left in him. Both my grandma and grandpa are over 70 years of age. They moved in with us about three weeks ago.
Due to an unexpected incident, my grandpa had to be taken to the hospital in the middle of the night via ambulance about a week ago and is currently undergoing treatment there. However, my grandma continues to stay at home with us, which is very taxing on us emotionally, especially my mom. My dad works overtime practically every day to keep us from going bankrupt, so he often comes home around 10-11pm and by that time his parents had already gone to sleep, so he's barely exposed to anything that's happening between the two.
Before they moved in we didn't use to have long-winded conversations and we just did our own thing, me doing schoolwork while mom did the chores, and I helped her out whenever she needed it. Now that grandma's with us and us alone, she insists on helping mom, but she is clearly saddened by her husband's state. She would not stop radiating that sadness to my mom in the form of her attitude, and it would seem like her drive to help is fueled by the fact that she has someone to vent to while doing so.
On the first day of her husband's unexpected leave, when my grandma asked mom "Is the food ready yet? I'm hungry." my mom replied "I'm working on it, I cannot cook it any faster" and my grandma told her "Oh, so you don't want to cook for me, I see." which my mom took great offense on. Just today my mom told my grandma that she might not be awake by the time she returns home from a hospital visit (she was taken there and back by my dad's sister) to which my grandma replied "Oh, so you don't want to let me in, I see." despite her knowing full well that I will still be home and could let her in regardless. She's also been speaking ill of dad's sister to us behind her back, which my mom also does not appreciate. All of this takes place when I'm not there to hear it myself, and on the rare occasions when I'm part of the conversation such things are never said by her.
All this looks to me like she's trying to guilt-trip my mom for petty things which are causing a great deal of anger and stress in her. Back when we used to visit them semi-weekly at their old home, grandma and grandpa would constantly argue, and grandpa has even told us recently that he'd rather be dead than deal with her any longer.
It's got to the point where mom asked me to secretly record a conversation between them to let dad know what's going on because she does not want to talk back to grandma due to her unconditional respect for the elderly. While we should generally be understanding with elders, if this trend continues, my mother will be an emotional wreck by next month, and I feel powerless in the situation.
Is this within the extent of what needs to be tolerated from an older person? What could I do to stop grandma from constantly venting to and taking her sadness out on my mom? Is there any advice I could give my mom on how to avoid the stress that comes with the situation?
Clarifications in response to comments
I'm a white male living in the east of Hungary, and the rest of my family are also white & lived in the same general area their entire life.
I'm only out of the house during school (7am-3pm) on weekdays and home the rest of the time. My mom usually leaves with me and my dad, and she arrives home at about 1pm, so earlier than me.
I'm turning 19 this month.