Yes, you can sleep overnight in the hammock stand. We recommend only one person sleep overnight in the Swiftlet at a given time. If you are very tall (6’4” +), you may run into the issue of your head bumping the bar while laying down. If that's the case, laying at a diagonal in your hammock will help prevent this.
We do not recommend using the Mantis with the Swiftlet. Read more about why, here.