I found your questions to be very perceptive. Unfortunately, the answers are probably not what you are hoping for right now. I can only reply from my own experience, but I hope it might help.
First, no, things will probably not get easier. In fact, it will most likely become more difficult and time-consuming and exhausting as time goes on. There will be routines established and ways to streamline the caregiving that may help make things a bit less complicated, but there are no magic answers.
My personal beliefs are that caring for someone you love is very rewarding in the long run, but that it doesn’t make it any easier while you are going through it on a daily basis. You don’t say how old you are or give your parents’ ages, but my view is that you are wonderful and generous to be helping out as much as you are right now. Five hours a day is a lot. I understand that your parents have the primary responsibility of your grandmother's care at this time, and I'm sure that your help is very much appreciated. But at some point in the future you may have full responsibility for one or both of your own parents, and then it will be your turn to devote more time. So don't completely sacrifice your own life right now -- continue to help them and help your grandmother as much as you would like to do, but also help everyone in the family by trying to ease the burden on each of you.
I am a full-time 24/7 caregiver for my 97-yr old father, who had a major stroke a year ago. I’ve actually been caring for him for almost 10 years now. Until a few weeks ago, I had no help at all and yes, I was exhausted and completely overwhelmed. I always felt that I could do it alone, but I finally made a serious effort to check on resources that might be available. I now have 2 therapists and a home aide who come for a total of 10 hours per week. It’s not a lot of time, but even that amount of time is helping both my Dad and me. It gives me time to take short breaks and it’s giving him a chance to be with other people. The home aide is now getting my Dad out of bed in the morning, getting his breakfast and getting him dressed (part of what you are doing for your grandmother) and I was told that we could get another aide to do the same thing at bedtime. I've decided to continue on my own for now at night, but might reconsider that option for the future.
I know how I've personally struggled and worn myself down, especially this last (very difficult) year. So my best recommendation for you and your parents right now is to contact every agency that you can think of in order to see what sort of help might be available. In our case, paying for private care was not an option. If your family can afford it, that is the quickest way to get help. But there are many other options through insurance, civic, and social resources depending on where you live and your specific circumstances.
I hope you will check on caregiving assistance -- sooner rather than later. The resources are out there and they really can help.
Good luck to you and your family.