Unable to post shared photos to Facebook business page

[Android Central Question]

I am trying to make scheduled Facebook posts to my Facebook business page. While any of the photos I have actually taken myself with my phone show up in the gallery when I add photos to my post, any pictures shared with me from my husband's phone (which I have already downloaded) don't show up in the gallery. I can see all of the photos (included the dowloaded shared photos) in the gallery when I go through google pictures, but when I try to add photos to a Facebook post, only the ones I took myself show up. Is there a way to post the shared photos?