Also, as for what Jem knows about Pet, I'm sure that Jem has probably had the chance to see the scars on Pet's wrists so he knows that something happened, but I feel like Jem probably wouldn't have asked about them. (Pet doesn't hide the scars, most people don't notice anyway). Pet has definitely talked about his large amount of siblings, probably by comparing Jem to them (sometimes Jem does things that reminds him of his youngest brother who now won't talk to Pet). Pet's poverty is pretty noticeable, since he is very stingy with his money.
I dunno, anything else you think he should know?