Sounds like you are doing everything great!It is a red heating lamp that is clipped to a ladder so I can raise to reduce heat. There is a thermometer hanging from rhe side of my brooder, showing 82 degrees.
I am still very new to raising chickens but I used this set up for all of my other chickens.
Also, I changed the pine shavings today. Nothing odd - still pulling from the same bag that I've been using since bringing these chicks home.
I would be tempted to add some electrolytes into their water once just in case. It’s odd that those two died. I’d also keep a close eye on the other chicks.