Oh, lots of fun flying with two!
Car seats are free to check so no worries there but you do need to figure out how you will get them from bagage claim and to your car upon your return. Hard to do when you are on your own. You can bring meds on board. I usually bring gravol and tylenol.
For DS, I would get him to carry his own back pack with one change of clothes (in a ziplock bag) plus his own toys. You can bring on two carryons. On my last flight I brought a carrier so I put DD in the carrier just prior to boarding, left the stroller on the jetway and carried on a back pack plus my boppy pillow. DS had his back pack with his own stuff.
I used a backpack as my diaper bag. I had a smaller bag with just wipes, a few diapers and my bag-it for dirty diapers. I would take the smaller bag to the washroom for diaper changes as there is never enough room in an airplane lav for you, the baby and the diaper bag! Pack changes of clothes in ziplock bags so if there are any messes, just put the dirty clothes in the ziplock.
Wrt Food, you are lucky because you can bring on baby food and bottles. For DS pack non sticky finger foods, same for V. By the way, you may not be able to bottle feed for the actual take off and landing as they want you to hold the baby, facing you. I never had too much of a problem with ears unless they were sick.
Wrt toys and entertainment - for V, she won't need too much as the first time on the plane is pretty exciting. May be a few things to teeth on. For ds, colouring books, play dough, videos are all great. When my ds was that young, I tried to not llet him bring toys that were too small as they get dropped on the floor and are hard to find.
Oh, if you can get a cares harness for ds that is great.
Lastly, once I get onto the plane, I take out the diaper bag, the toy bag and something for ds and put it in the seat pockets. I also make sure I have the air sick bag handy. Yes, I have had ds get sick on me one hour into a 5 hour flight. Don't be shy about asking flight attendants for help.
Safe travels!