Photos Sending Out Of Order - iMessage Fix
When you select images from the Photos app to send via iMessage, there appears to be no way to control the order in which they are received. I’ve seen countless threads voicing this issue and I personally experienced it.
BUT there is a workaround. Instead of selecting/sending images from the Photos app, do it directly through the Messages app by pressing the little Photos icon above the keyboard. This allows you to send the images by order of selection.
A con of this method is that you can only select images from your Recents album.