How do you fill in the required categories for Parent ASINS

For example if you’re selling two pictures, one is of a dog and the other is of a cat, what do you put as the title of the Parent ASIN?

What if the size of the products are different and the size is what people specifically search for when searching the products, do you put both sizes in the title? What do you put for the size of the parent ASIN? All of these fields are required and I am not able to proceed with listing without it.