Do you think Orson was Clara's great-grandson?
Either that, or he’s related/connected to the Doctor.
He has Danny’s last name and said his great grandmother told him time travelling stories so id assume yes
He didn’t say great grandmother, just great grandparent…
Exactly.
What we can safely assume here is that Orson is Danny’s great-great-grandson, so that either means:
- the gg-grandparent he meant was Clara
- which means Clara and Danny got married/had kids
and that’s how he will be connected to Clara, or
- the gg-grandparent he meant was Danny
- which means Danny will be a future companion of the Doctor’s
and that’s how he will be connected to the Doctor.
EDIT.: Adding the dialogue from the episode:
CLARA: Orson. Do me a favour, take my advice - when you get home, stay away from time travel. ORSON: It runs in the family. CLARA: What? What? Sorry, what do you mean? Runs in the family? ORSON: Nothing. It's just silly stories... one of my grandparent - well, great grandparents--