Here the sentence is "My father has to eat." When you use the "Have to" form in Hindi, you use object pronouns, instead of subject pronouns. I have to eat = मुझे/मुझको खाना है, She/He has to eat = उसको खाना है. So when talking about a specific person, add को after their name or however you are referring to them, in this sentence मेरे पिता. Don't think of it as literally meaning "To" but just as the second kind of pronoun that some sentence structures use. What problems have you been having with से, any examples?

That would be यह मेरे पिता का खाना है