Our cats are not related (other than being adopted sisters, you know) but came from the same place and had known each other from young kittenhood so they get along and are often curled up together on the bed at night. Both like to get under the covers with us, usually during the day if we're napping. The cover is important: One in particular demands that I go sit in the recliner, put my legs up, and put on the blanket.
When we go to our 2nd home, she gets in her carrier merely by being asked to do so. She then cries all the way there. Once we've arrived and she's figured out where she is, she goes and sleeps in the carrier. Apparently the problem is just the door being closed.
Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.