Looking for advice/tips/etc flying DL; mods please move if required

Taking my boys (2.5 and 1) from STL to SAN. First time traveling solo with them (happy to finally take a vacation with them as the soon-to-be-ex would never allow me to go on the trips she took them on, but I digress)

Outbound, since I'm traveling alone, were flying F; on the return a family member is flying back with us so were going Y (plus the trip back is much shorter). 2.5 year old has his own seat, 1 year old will be a lap child.

I'm thinking that transiting the airport/going thru security/connections/etc. I will have them in the stroller. However I'm debating about checking the car seat because I can't fathom being able to get thru security with carryon, the kids, and being able to carry the car seat. Though I am thinking that it would be easier to have 2.5 year old in the car seat on the plane. Any thoughts on how to resolve this?

Requested upgrades on the return (SANSLCSTL); I am Gold, and know we will clear at lowest level but with companions do you clear as lowest level Gold or behind Silver? Does having a lap-child in reservation impact anything? I'm really more hoping to clear into Comfort+, but just curious how it works with companion/lapchild.

Planing on having plenty of food/snacks/toys but any other suggestion/tips are greatly appreciated.