Ok, I totally screwed up. Sometimes you just gotta keep making the same mistakes over and over until you’re reat to learn the lesson.
In my case, the lesson is to make the mortise first before cutting the pieces to the final size. Because it is too close to the edge, it just caused the wood to split. Oh well. I am made of mistakes after all. I will learn this someday, I promise. Also I was being overly ambitious in making so many mortise in one little space. The idea was to cut the box is half lengthwise, (even though I am totally not proficient in making rip cuts.) I have a new idea on how to avoid this, but I’m going to let the idea brew a little more.