Hey, @ane marie photography. Welcome to the Lightroom Community. I'll help you figure this out.
What version of Lightroom & the operating system are you working on? Lightroom Desktop does not have support for external Brush presets at the moment.
If you're using Lightroom Classic, did you create these brush presets or get them from elsewhere?
Check the exposure in the brush preset. Exposure at the lowest values can appear really dark and almost black. Please attach screenshots of what you see when you use a brush preset.