So... Like an idiot I moved a sims family to a new neighborhood by putting the lot they were living in into the Lots & Houses bin, then placed the lot in Veronaville. When I tried clicking on their lot, they were gone and the house was for sale. However, in their old neighborhood they both have family ties which are still in existence. After reading the SimsWiki I found out that it will cause lots of errors if I don't delete Veronaville. But if I do could that hurt my game more since both these sims have multiple family ties in a different neighborhood?

You've already one the damage and created the errors, I'm afraid, so whatever you do now (as long as it doesn't involve moving more families/placing that family into a 'hood again) can't really make things worse. The copy of your family in Veronaville isn't linked to their original neighbourhood at all any more - which is why the neighbourhoods are now corrupted - so if you want to delete Veronaville, that won't do any harm.

Alrighty. Do you have any idea why the family is gone? They are no longer on the lot, or townies (though they are listed as town residents, but I can't invite them over or anything). I'm guessing there's no way to get them back?

Both hoods are now corrupt which means anything can happen including disappearing sims.. The hood you took them from and the hood you moved them to. If you want to save your sims you will need to extract there likeness with SimPE and jot down everything you want to keep about them so you can set them back up as they were. Make sure if you do extract sims that you clone them in body shop and delete the extracted sim, keeping the clone.

Are you saying that they still exist in the old 'hood but not in Veronaville? Or are they gone from both?

I see.. Unfortunately I have a Mac therefore SimPE isn't available..

They're gone from both, but if I use the "Make Me Know Everyone" cheat on any residents of Veronaville they will show up in their contacts but you aren't able to call them/summon them/invite them over. The only trace of them in their old 'hood is their family ties.

Do you have a backup? If not it sounds like they are gone. You would probably do best to reset your hoods (if they are both game hoods) and start of fresh.