You can perfectly air travel on your second trimester. Actually it is the best trimester since you are very energetic and those horrible first trimester symptoms are gone. hopefully. GO!!!!!
I flew at 24 weeks and it was totally fine! Tell the airline at the gate you need to be by the bathroom and try to drop your preg with twins. I was bumped to business class, maybe you would luck out and be bumped to first! Just carry very light and make sure you will have help with picking up your bags.
I agree second trimester is a great time to travel, I might be flying at the end of 2nd/beiginning of 3rd trimester before it becomes too exhausting. Just exercise your legs because of the risk of DVT (it goes for everyone not just pregnant women). You should be fine.