As paterfamilias is a title in English, one should be able to say "He is paterfamilias"
I have never heard this title used as part of the English language.
I have, though in my Roman history books. It's the same way toga is now an English word, albeit very specific in meaning.
Basically, some words in Latin do not translate well. Forum is an excellent example. It's often translated as market, but it would be best translated as: Meeting Center/City Center/Market/Mall/Parade Route/Public Space. So, you can always safely translate it as "Forum" into English. Similarly, if you have a Mexican Restaurant named "Casa Fiesta" in your town, you don't suggest to your friends that you go to the Party House, but rather, "Let's go to Casa Fiesta" because it doesn't need to be translated. You wont hear Paterfamilias outside or Roman/Latin contexts though.