I opened up your screen cap. I lifted the tone curve up a bit in the upper region. PERFECT WHITE. You are not that far off. Your WHite Balance however is what we cal "Eff'd"... 4,700 Kelvin??? What???? NO wonder it all looks so whacked. Your image does not look "dark". I mean, if the Minus 0.35 stop negativ exposure comp is considered "dark", then yeah...
Again, these images are not dark--but they DO lack CONTRAST...Your Tone Curve is "eff'd up". Set the WB to 5100 to 5300, estimated. Grab the curve and lift it a teensy-tiny bit. Problem solved. Bkgd goes the right tonal value. AND looks pure white.
COPY settings. Select all other images. PASTE settings. Whole set, done in like 2 minutes.