Is keeping pictures of my deceased brother and watching his videos harmful to him, and what is the ruling on that?

Photography and video (including mobile phone photography) are permissible if they do not depict something forbidden, because they are a mere capture of a reflection and do not involve imitation of Allah's creation. Nevertheless, it is preferable to avoid them if there is no benefit, as a way of avoiding disagreement. It is better not to keep such images, especially if they rekindle sorrow.