I can only send 1 at a time. Also, I have to take the photo FIRST then share or attach it. I used to be able to take a photo from the text msg but for some reason that is no longer an option.
In the stock Samsung Messages app, click on the paper clip icon, and then options for Camera, Gallery, and Other appear. Clicking on Camera should open up the Camera and then from there take a photo that will give you the option to add it to the text message.
From the gallery long press on a photo then select all the pics you want to send and then select share and then select the stock messages app . Usually I can send about 4 or 5 pics using this method.