Okay, I'm a little confused by the OP, but I'll try to provide answers I know. Yes, you can bring your own carseats, and they do not count as checked luggage or carryons, provided they go into a paid-for seat. In your first post, you mention that your kids are all young enough not to require a paid ticket. However, in order to use their carseats, they must take up a seat, and the airlines will charge you for that seat. So your choices are:
- Don't pay for tickets for the kids, and let the adults in your party keep them in their laps. You would then need to check your carseats like luggage, if you wished to bring them along. As other posters have mentioned, this will require breaking up your party throughout the plane to comply with the need for one oxygen mask per passenger.
or
- Pay for tickets for the kids (some airlines offer reduced pricing for kids). This way you can keep them all nearby (probably), they each have their own seat, and you can strap their carseats comfortably into the airline seat, without them being considered carry-on luggage.
Since I usually fly SWA, and we can get dirt-cheap pricing to Orlando from Louisville or Nashville, I usually get tickets for my toddler, and bring along her carseat. Fortunately, my 2 girls are 4 years apart, so only one has needed a carseat at a time when traveling by air. I've never had to bring 2 carseats on a plane (though I still have a booster seat for my oldest in our car).
As for strollers, yes, you can wheel them down the jetway to the plane entrance, fold them up, then FA's will store them for you during the flight, and put them back on the jetway at the destination.