I think the only thing you can really say to Airbnb is that you did not leave the bathroom, nor stove in that condition.
As far as wanting space to cook, etc. unless it is asked before booking the reservation: “Are there scheduled times for guests to use the kitchen?” - the host probably just assumed you wouldn’t mind being in the kitchen with the Dad. I can almost bet the friend stops by often to hang out with Dad and they are just used to “strangers” being in the house. It wouldn’t cross the Dad’s mind to introduce you to his friend if Dad doesn’t have a really friendly personality.
If I was concerned about bathroom/kitchen usage times, I would have asked the host before booking the apartment. That way I would know if it would work with my own plans/schedule.
I don’t really know what to say about finding the dirty utensils in the kitchen cabinets. I have had guests put back dirty items because they were too lazy to clean them. If the Dad used the items and put them back then that is disgusting. But it’s possible a previous guest had just left and shoved their dirty utensils back in the cabinets. Or they just did a half ass job cleaning them.
I am going to guess the Dad was upset about the dirty dishes from the previous night’s dinner being left in the sink overnight. So then he woke up and was cooking for his friend with the kitchen not being clean. So he just put his dishes on top of yours.
So then when you and your DH went in late morning and cooked more, and left more dishes on top of his dishes, then he became very upset. Then he probably started analyzing everything else and what was a normal “used” bathroom, became a “filthy” bathroom.
I don’t have any experience with the resolution process. I think if you don’t accept the charges then Air will intervene. Did the host have a damage deposit listed?
The fact that he smelled like a pack of cigarettes, was sweating, sat in your car giving directions, had bottles of meds in the kitchen, had his friend over in his house eating while you were trying to cook, etc. isn’t really relevant. That is all part of the chances of staying in a shared home.
The one thing you could mention is to show Airbnb the conversation where the host agreed for you to get the weekend rate at the weekday rate. Let them know you were not reimbursed the $12 difference. So under those circumstances then you feel $12 is a fair trade off for the dishes he had to wash.
Let us know how it turns out.