Me and my fiancé are traveling by ourselves to Las Vegas and won't have a witness. Will someone at the courthouse be able to sign as a witness for us?

You have to have a witness for the ceremony only. The ceremony can't be held at the courthouse unless you know a judge. Depending on where you have your ceremony...they might provide a witness.

I'm not sure, but I think that could happen if you want that. It's better to bring y'all relatives to witness the marriage.