As a grandmother raising two of my grandkids, I feel you. My husband helps a ton as I'm still working, so he's doing the school runs twice a day, picking up groceries for dinner, keeping the washing machine fed. Retirement? Vacations? Even a night out with friends? Nope. My husband is 73 and this not how he saw his retirement--we can't even get to see our other grandchildren as much as we want to. And I'm 64 in a very physically and emotionally stressful job (Special Education teacher) and I need to retire at some point, but we can't raise two grandkids on our retirement funds. And my grandson has special needs, as you can see from my signature. We even may have to pick up and move to a bigger house so they each have their own rooms. I mean, how long can my granddaughter be expected to sleep in my room? (My husband has his own room---epic snoring and he worries so much about that he can't sleep if he knows he may be keeping me awake).
Your grandkids are too young to really help much with the chores other than to get the clothes anywhere near the machine, carry their own dishes to the sink, have a toy clean-up party after dinner, etc. I had to learn how to parent again, and I never had to deal with the kinds of things with my own kids that I'm dealing with now. Ross Greene's books "The Explosive Child" may help, and establish routines and structure with their buy-in. Have a predictable schedule and sameness from day to day will probably really help the kids in time. My husband and I have adapted to the increased demands, but I'm not going to lie: we are tired and in bed by 9. Do you see any light at the end of the tunnel? We've come to realize that my daughter will never be in a position to raise these kids. She's around here and there, father is out of the picture for all practical purposes. I go from being extremely angry and frustrated with my daughter, glad I can have my grandkids with me instead of constantly worrying about them, fear for my future if my husband or myself gets sick or just can't do this anymore.
Bless your heart and those kids are so lucky to have you. I ended up in foster care because my grandparents couldn't/wouldn't step up to help. Stick around--lots of support here.