I would like to know the answer to your questions also! I have 2 Yorkie boys. They used to go into the same carrier and Ive flown with them twice over the years. They did fine when they were in the same carrier. Then I had one of them fixed and he put on a whopping 50% of his weight and now they are too heavy & big to fly together in the same carrier and too heavy for me carry in the same carrier. On our flight home from my mothers house my bf took one and I took the other. The airline was complete jerks and made me stick them under the seats and told me to leave them there and leave them alone. Well my little guy who has separation anxiety, went into complete panic mode, even with a double dose of benedryl. He FREAKED! He actually dug at the carrier netting so much that he got OUT of the carrier and I had to hide him under a blanket in my lap for the flight and then try to get him off the plane without him climbing out of his damaged carrier. Poor baby!
If I ever fly with them again, I would like to know what to do to make it easier on him. It stressed me out to see him like that. My other boy just laid in his carrier quietly and slept! Hes a good good boy!