Alright, this is a biggie! There are no perfect relationships of any kind. But the degrees of dysfunction can vary.
Sometimes, the family evolves over time and looks back at their troubles and can now laugh. If this is your family, you're good to go. If you can be around each other and the past doesn't haunt you, you have been able to heal and move forward.
You will have to give a lot of thought to going back to living under the same roof as your parent if there was serious dysfunction.
In the event of a truly dysfunctional family, it will never get better. You couldn't live in harmony in the past. How would anyone expect you to do so now? The ill feelings are too great to overcome. Especially, for family members who have had to go into therapy for their own well-being. Your well-being has to come first. And don't let ANYBODY try to give you a guilt trip.
You didn't have anything to do with being born into your family. You've survived those years. Do not, I repeat, do not put yourself back into that environment. When we are around our parents, we do digress to our childhood memories. That's a fact.
All the dysfunction will rear up again. You will backslide. You are too important for this to happen. Find other ways to help your aging parents. Call services in their area to get assistance. Whether it be home care, assisted living or a nursing home if that's where they need to be.
Yes, it would be nice if all families were of the "Leave It To Beaver" fantasy. But that isn't what real life is like. For troubled families, life is fraught with bad feelings. They don't go away. Some will say they are over it and have forgiven.
So why do they still have nightmares about their childhoods? This happens. Unfortunately, some families need to stay away from one another. Do not blame yourself. Take care of your life. And find someone else to take care of your aging parents.