I find it best to ready the boat before doing anything else. This ensures that their priority will always be to beeline it to the boat and get in.
As far as releasing them goes, my experience is as such:
- Releasing the Gnomes first... They just leave. Since they don't care about anyone else.
- Releasing the Tieflings first... They will hang around and want to help release the Gnomes.
- If you release both quickly/simultaneously (By using a character at the back wall of each cell with bombs/Eldritch Blast ready to break the walls) they will generally both just head directly to the boat.
Normally what usually happens is I have guards come around while waiting for the Tieflings to make it all the way to the boat. BUT if intercepted quickly enough, both the Tieflings and the Gnomes will be grouped up by the boat and won't actively engage with the guards. So it ends up being fine to just beat up the guards and then take the boat out.
I haven't really figured out a way to get them all to the boat and escape before the guards get there. It's probably possible with good timing of guard patrols (After having prepared the boat and broke the 2 groups out simultaneously). There's probably other things that can help, such as using Arcane Lock on both cells (So the guards can't open the cells and have to go around to the cliff in order to make it back there) and using Silence on the walls so breaking them doesn't make noise to alert the guards. However, I've not tried such things as of yet.
