My husband and I have traveled cross country several times with our now 1 year old. We always buy him a seat, so we have his carseat, stroller and carry-on. I have traveled with him alone, so I think that sort of counts as traveling with 2 of them and 3 adults!
A couple of ideas- we always try and use a backpack as the carry-on, as this allows you to just put this on your back. It usually means that I don't bring a purse, but just use the backpack for everything. We have both a regular backpack, and a backpack-style diaper bag. That takes care of the carry on problem.
You can gate-check the stroller. Some airports allow you to do this at the entrance to the gate, and some allow you to take it all the way down the jetway and check it at the entrance to the plane itself (this is much easier). Either way, just take the stroller through security (you will have to fold it for x-ray purposes) and then tell the agent at the gate that you are gate-checking the strollers. They will tag the strollers and give you a copy of the tag. When you arrive, the stroller will be just outside of the plane door. That takes care of the stroller.
As for those bulky carseats, we have always found a way to attach the carseat to the stroller. We rest the bottom of the carseat on the stroller basket, with the carseat facing the stroller and then use either the tether cord or a bunjee cord to attach it to the stroller handle. This is rather bulky, but it means you can just wheel the stroller through the airport with the carseat attached. You may have to play around with this idea, depending on what kind of carseat and stroller you have. Also, we have found that you have to carry the carseat above the seats in coach to get down the aisle. For that reason, we always request to board as early as possible, to avoid banging other passengers in the head!
In general, we have found that most airline employees haven't gone out of their way to help us carry stuff. However, when I have traveled alone, I have always found other passengers to be really helpful!
Hope this helps!