Air travel with a CARES harness and a RF Scenera

I'm flying out to CA in the 14th with my 3y1m DS1 and 5m DS2 so I'm going through all my final preps to make sure everything is in place. I'm going to be the only adult so I'm reducing stuff going on the plane with us -- especially being as we have a connection. So I'm planning to only take a Scenera on the planes with us for DS2 and use a CARES harness for DS1.

I pulled the CARES harness out the other day and practiced using it. I noticed that the strap that goes around the back of the seat has to go over the tray table if its recessed. We're flying United and I think all of their tray tables are recessed. Has anybody used a CARES harness? How did it work out for you and did you have any issues with the tray table thing?

Also DS2 will be RF in the Scenera. I've done a seat belt install in my husband's car but I'm concerned about how the seat will install with an airplane seat belt since they put the buckle right in the lap instead of at the side. I'm not sure where the buckle would end up with going through the RF belt path. Anybody with experience on this?

Thanks in advance!

ETA: I forgot my last question. For the first leg (Dulles to LAX) we have all three seats side-by-side. I'm thinking the RF car seat will have to be by the window, I should be in the middle, and DS1 by the aisle. The second leg is only ~1hr and we have two seats on one side of the aisle and one on the other which is the entire width of the plane. I'm not sure how I should do seat positioning there. Car seat in the singleton so I can keep better control of DS1, maybe?

The Scenera buckle typically ends up under their legs, but mine have never complained about it. It's an easy airplane install. The cover is super easy to pull back, so you can access the buckle.

You aren't supposed to be allowed to install a car seat in an aisle--I don't know if that applies to a CARES also so I don't know how your first flight will work out. And your situation on the second flight is further complicated by the fact that the window seat and aisle seat are the same seat!

Personally, I like to travel with DS in the row ahead of me (he sits in the window next to a stranger) and DD sits in the window seat next to me. Since DS is RF, he can see me and I can reach over the seat to him. I have found this to be much more convenient than having him across the aisle but we have never flown a plane as small as the one you are describing. If they will let you put the car seat in the aisle/window seat, then that could work well.

That's good to hear on the Scenera airplane install. I know lots of people use them for travel but this will be my first time. I'm just hoping no one hassles me for using a RF install.

So the reason car seats have to go next to a window is to not block passenger access to the aisle so I would imagine a CARES harness would be okay on the aisle since its just a set of straps. I didn't see anything explicit on the United site or in the CARES material.