I'm with the others in the belief that the bunks will go unused, pets will generally tend to follow the owners unless the cat happens to be an aloof one.
If so, you will get a lot more usable space with a non bunkhouse trailer.
In order to get a better idea what fits for your usage, you may want to rent a trailer a couple of times for a 2 or 3 day trip. Try a couple of sizes and configurations at least one with bunks to test the pets, and use that insight to make your final choice.
Since you are looking as new as 2015 or 16, try checking the manufacturers websites for construction and capacity info. Many 2015 floorplans are still in production and weights generally wont have changed drrastically. Since you are west coast, I would look at Outdoors RV and maybe Lance. Both good quality and available in your region.