First, good for you for having family dinners and encouraging conversations!
Be it good or bad or right or wrong, there was no topic off limits at dinner. My DH and I wanted to be able to talk to our kids about anything and have them come to us about everything, so we didn't limit the conversations. Now having said that, it was never really gross or disgusting!
Since you homeschool our 3 standard questions may not work. What did you learn today? What did you have for lunch? And who got in trouble today? OK, we don't encourage gossip, but it's incredible how much they will open up when they can talk about someone else. ;)
We also discussed current events, music, sports, TV, books, pop culture, etc. Even now, my kids crack me up! They are 22 and 18 so I won't share some of the discussions. But again, if they know the environment is a safe environment, they will open up.