It sounds like you are ready to get a D. When that time arrives, it brings with it a lot. ...many emotions. ...some good, including the feeling of regaining some control over your life again.
When I reached that point, I asked someone that was involved in the court system who they would recommend as a good divorce attorney. I met with the person they recommended and was comfortable right away, so that part was pretty easy for me. I hope the same is true for you.
Ask the attorney where you start. They will guide you.
Telling the kids is the hardest part. I think you will need the custody and living arrangements finalized before you tell them. They will want to know, naturally, how this will effect them.
My kids are a little younger than yours. Here is what I chose to tell them. "I have something important to talk to you about right now. Let's come over to the kitchen. "First, and this is very important, you haven't done anything wrong, so what I'm going to tell you isn't about you. It's about mommy and daddy. Mommy and daddy don't love each other as husband and wife any more, but just love each other as friends. So, we can't be married any more. Mommy is going to live in her apartment. The two of you are going to continue to live here with me. You'll see mommy mostly on the weekends. But everything will stay the same for the three of us. You will stay here with me. That's what I wanted to tell you. You can ask me any questions you want to."
Yes, it's a heartbreaking talk, but I got through and they handled it just fine. It's been a year since the divorce was final, and the kids have done fine.
Good luck to you.