Airline/Travel car seat situation..

[Crew&West]

Okay, so we are going on vacation in March and my sister (where we're going) has a Evenflo Triumph that we can use and she is going to go buy another seat for my ODS.

First question: I'm curious, if anyone has a 3yo who is about 35lbs that fits in the Evenflo?? Surely he would fit?! He's about 37-38in tall.

Also..I REALLY don't want to haul them around the airports. We have a layovers and we are not checking any bags so we will have about 3-4 bags, 2kids, my backpack/purse, hubby's backpack, and the kitchen sink. My ODS is 45-46lbs clothed, 46in tall and 4.5yo. Can I use a CARES for both of them on the plane???