I feel the meanings of "will" in the sentences below might be slightly different.
I will buy a new car which is made in Italy.
My father will buy a new car which is made in Italy.
I think when you say "I will..," you can express your own will, and it doesn't always indicate my firm decision. But when you say "He will..," I think it might mean "I think he firmly decided to do something" because I am not he, and I can't directly know his will.
Or it won't indicate his will at all like in the sentence "It will rain tomorrow,"
or it might mean "My father will buy, and not other person will buy."
So, I feel the second one could be more natural if it is like this, if I want to express my father's intention:
My father is going to buy a new car which is made in Italy.
Am I correct?