Next, go to Cambridge and the University thereof to get on with doing your degree. Try Engineering - it's nice enough. Better yet, do Engineering but try to fool people into thinking you do an arts subject. It is perfectly acceptable to be a closet English student. Do your sister's work when you've got a couple of minutes.
Parents tend to like to see all the architecture around the place, since there's plenty of it.
Go for a wander around. Remember that libraries are non-smoking so this could be a good time for your dad to resaturate with nicotine if needs be. Pollute local atmosphere. Once you've done enough of the Prodigal Son routine, send your parents home. Go to where you're living in Cambridge and welcome whatever guests drop by.