Mailbox not working and can’t use certain dialogue

@BadGalMsJo okay I've taken some images now, to get your Sims saved to your Library go to Manage Households and click on the household you want to save so that you get a recent version of them, so if you've transformed one into a mermaid for example. The first version you made of them when you started a game may already be in your library, but that will be their brand new unplayed version and you'll probably want the most recent. In their household panel click the pencil icon to "Edit, add or remove Sims from the household in Create a Sim". Once in CAS click the Save Household button in the top right corner (pictured). You should get a box pop up like the second attached image. Click the button in the bottom right hand corner as the image shows and Save Household to my Library. Then in live mode/build mode or manage worlds in the top right hand corner of the screen click the Gallery lightbulb button "Open the Gallery". The first tab is the Gallery with other creations from other players, press the RB bumper on your controller to switch categories and check your Library. Your household should be there as you've just saved it (pictured).

Then go to your New Game and return to the Gallery button and back to your Library. Locate your saved household and click on them. This time in the bottom right hand corner of the screen you'll see a Place Household button, if you click that it will take you to Manage Worlds and you can place them wherever you want them to live. You can also do this with their house in build mode by selecting the Folder button on the tool bar for Save to My Library>Save Lot then again in the bottom right hand corner of the screen click the arrow button that says Save Lot to my Library. Then in build mode you'd open the Gallery again and go to your Library and place the house.

There's a tutorial for the Gallery itself if you haven't used that before just go to open the menu as if you were going to Save and click Lessons>Gallery.

Hope this helps!