Ernest. The images from your camera are around 4K in size, so you don’t really need to change their size at all really. Also forget PPI. If you take your 3965 * 2478 pixels and reduce PPI to 100, then your image size is 1322 pixels on the long side and it’s no wonder your seeing unacceptable results.
If you must resize the images at all, ignore the Pixels Per Inch and adjust to 2304 * 1296. That gives you a HD size plus about 20%. If your computer can handle the images from your camera, don’t downsize them at all.