HEIC image format was introduced by Apple for Live Photos. A Live Photo captures a 3-second moving image.
Non-Apple devices will not be able to open or view those files without using a third-party program or app to convert them to a viewable format like a JPEG. We recommend you address this issue with your co-parent and ask them to try saving the file in a different format and then re-attach it to the message to download and view.