Your father is a strange man. How did he come up with a strange saying about kittens carrying coffins? Why not say that all four lucky cats came to wish him a fortune? Businessmen in Japan and Guangdong, China like to put a lucky cat at the checkout counter, symbolizing a prosperous business. Your family can also buy a porcelain lucky cat and put it at the cashier to improve Feng Shui, so that your father won't have that strange idea when he is happy.
The kitten was born in your house because her mother's kindness made her feel safe. She can also help your family catch mice and kill cockroaches. This should be a good thing.