Can I use Unsplash photos as part of a product to sell?
It's technically legal, yes, but we'd be careful how you package the photos. If it looks like you're selling the photos, we'd personally recommend not doing that. Other sites have tried to sell photos from Unsplash and the Creative Commons and Unsplash community have been very vocal and aggressively against it, since you're directly profiting off of someone else's work, without their permission.
However, if you're including the photos as examples of how you can overlay the icons or actions and presets on the photos, that's totally okay. The main thing to think about is: are you using the photos in a remix-able way, or are you adding something to them when selling them?