thomas schell's name in the art store

At the end of the last reading, the grandmother says that the grandfather came back after the dad's funeral.

I don't know if anyone else keeps wondering about how the name "Thomas Schell" was written everywhere in the art store, but I think that it was the grandfather, not the father, who wrote his name there. Maybe he's been there the whole time? Maybe he's the renter? What do you guys think?