To be honest, most of those images have been used hundreds of times, and the models are probably OK with that, assuming your stories don't make them look bad. I think for Unsplash, it's an opt out of legal liability, because they do not ask the photographers to upload model release forms (commercial photography sites do). I deleted and replaced almost all photos like this when this first came to light, but I used one the other day, just because the risk is so low and it suited me.