Questions about lights and sparkplugs

Two quick questions for those who are more mechanically inclined:

I own a 2016 Kia Soul EX GDI.

I think I need to replace two of my sparkplugs, as I'm getting misfire errors on my ODB2 reader. Should I get both replaced or all four? Also, is there a recommended brand of sparks I should use?

Second: I think my brake lights are out - the strip above the hutch door still work but when I hit the brakes, the back lights don't brighten as they should. All other lights work fine, so I'm wondering which lights in the back would need to be replaced?