NPC Problems: Uni Townies and the Mailman

I decided it'd be best to put both of these in the one topic.

Issue 1: University Townies such as the mascot like to come into the houses in my main neightbourhood, but act just like they were at uni. As such, they let themselves in and run around yelling at my sims, playing my guitars and watching my TV until I manually tell them to leave.

Issue 2: Every morning the mailman will walk down the path and stop in front of my mailbox. He'll just stand there for a few hours. I'm not sure if he actually leaves on his own but every time I load up a house he'll appear the next morning. This means I don't get any bills.

Does anyone know of any reasons this might happen? I don't think I have any mods that affect either of these sets of NPCs directly, but it's possible there's a conflict I haven't noticed.

- PageCaek