I feel completely broken

Let me preface by I love my children more than anything but I feel like I am absolutely failing. I have an almost 4, almost 2, and 4 month old. My oldest is just an absolute mess. She sucks her thumb non-stop (despite every trick in the book), she STILL will NOT poop in the toilet and has accidents all the time, she is so rude to everyone, and is just so unpleasant. I don’t understand where she gets it from. We are super polite in this house. It takes every ounce of my self control to not scream at her for being straight up disobedient . I’ve taken the big little feelings course and it’s not working. I’m following it to a T. I also started a preschool program with her to add more structure to our day. Then my son has a speech delay. Despite all the activities I make and strategies I implement I feel like he’s making no progress. He also has a horrible temper. My baby is so sweet and i feel like I don’t deserve her. I wish I could give her more attention. I also think about how sweet she is, but then feel dread that she may end up like her older sister. I just feel so broken, ashamed, and just completely depleted.