1) My father has a factory ...... makes bread.
2) The building ...... was on fire last year is being rebuilt now.
3) My father introduced me to the pearson ......designs a web page.
4) An Interior Designer is a person ...... designs the inside of a building
Use "who" for people and "which" for things. If the relative clause happens to be a so-called defining relative clause -- which is the case in all of your examples -- then you can use "that" for both people and things.