I am not sure if you have left or not, but I just got home from my daughter's first roundtrip plane ride. She is 13 months old and has an easy going personality. However, the plane trips were horrible. My friend's 24 month old did better, but he is old enough to better understand what is going on, take lollipops, etc.
HOWEVER, I do think that the trip went poorly because she has ear problems. She had tubes in April and they have been wonderful. I even went to the Dr. to have her ears checked and got the "ok" to fly. I think she was in a lot of pain and inconsolable. I was upset and stressed. However, the flight attendants were wonderful. They found a mother with some ear drops to help. I was not sure what they were, but after 30 minutes of pacing, swinging, rocking, etc, I was desperate, so I used them. They really helped. It is called Opticaine, and it is an Rx.
I called the Ped. after we landed and found out that she cannot have the drops because she has tubes (oops), but this one time should not be a problem (phew). Their only suggestions were everything I had done - packed a bunch of toys and snacks she had never seen before; try to get her to eat or drink during takeoff. She no longer takes a pacifier or bottle. She was mid-sippy cup when she started to get upset. For the trip home, I decided to give her the Benadryl. I felt bad about it because it was against what I would have preferred to do. Also, I did not have time to try it and was scared it would make her hyper, but could not imagine anything worse than our departing flight and tried it. Our trip back was better. She still got upset, but I was able to console her and get her to rest on the way home.
So, after that long story, my suggestion would be that if the boys don't have tubes, skip the Benadryl and get some Opticaine for an "in case of emergency, break glass" use to help with any ear pain. I don't know if you really need the Benadryl if it's just for the concern that they could be difficult to manage on the flight. It sounds like they will probably do great.
If they can fly without the ear pain giving them much trouble, I would go with the previous recommendations of lots of snacks and toys to entertain them. I went to the dollar store beforehand and really stocked up on toys and books. It was inexpensive, and once she was calm, they gave her something to do on the plane. In addition, my friend's son (who does not have ear problems) flew quite a bit before the age of 1. He was fortunate enough that his ears did not hurt and just needed to be entertained.
Good luck and enjoy your trip!