I have an inexpensive thermometer on the floor of the brooder in the warmest spot to make sure the temperature is warm enough--85-90 degrees F for week olds. Also make sure they can get away from the heat to a cooler spot.
As far as the sneezing, they might have a respiraatory disease such as infectious bronchitis or mycoplasma gallisepticum (MG.) Those come from carrier birds, and MG can also be passed through hatching eggs. MG may also cause watery or bubbly eyes, and swollen eyelids. Tylan 50 injectable given orally 0.2 ml twice a day for 5 days to help treat MG. IB is a virus, so will have to run it's course over a month or so. Deaths can be common in chicks with either of those diseases. Very sorry for your loss.
Dusty bedding, poor air circulation, ammonia odors from droppings,and wet bedding from spilled water are some things to avoid to help prevent respiratory problems and sneezing.
