Sounds like you are avoiding the problem. When you said your father is a "hoarder" it struck me as too casual - as though you had dismissed it. Your mother's behaviour suggests hoarding is a problem for her as well - and just like you, she is avoiding the problem. She is using your home to escape the hoarding at her home. She is also using her grandchild to try and help her husband maintain some kind of social life.
I don't know how bad your father's hoarding is, but if his home is not safe for a child, it is not safe for your aging parents. I don't know if your mother is also a hoarder, or just an enabler, but you need to consider her role in this.
Please try and understand how awful hoarding is - for you. It is embarrassing. It is scary. It is overwhelming. It is disgusting. YOU love your parents but you don't want to go to their home. YOU want them to come to your home where everything is fine and you can all have a "normal" family life. YOU are afraid.
Once upon a time, I was in your shoes. Since it happened back in the 1970s when no one had ever heard of hoarding, I had no idea what was going on. All I knew, was that I'd always loved going to my mother's home. We were very close, but one day, Mama started making excuses, why I couldn't visit her. On and on it went. Eventually, I decided to confront her - drove to her home, unannounced and knocked on her door.
When Mama opened the door, the smell coming out of her house made me gag. Nonetheless, she let me come in - and that's when I saw the problem. We had a terrible argument that day. I stood my ground. I told her I was not going to give up our time together. She could clean her house out, or I would do it for her, turned on my heels and left.
One month later, I spent three days at my mother's home, cleaning out her house. OMG !!! Yuck! Gag! Puke!
After that, our relationship went back to our happy normal. But I kept an eye on Mama - and when I saw the first signs of hoarding - I put the fires out.
Clearly, you love your parents as much as I loved my Mama. Since they are the only parents you will ever have, please confront the problem. Roll up your sleeves and do what needs doing. Clean your parent's home and then keep it that way. Show your mother she is not alone - she has an ally in you. Show your father you love him enough, to stand up to him and clean his house.