Is it the expense, or is it the time thing in terms of when he bought them? You mentioned both.
You may have known her since she was two but he's been there the entire time. He is allowed time with just him and his daughter, especially if you two were planning on bringing in a baby, because she needs to feel like she won't be replaced.
And you are her step mother. There's nothing wrong with that word. I call my step dad, my step dad to others, and by his name to his face. I do not even call my biological father dad, and I barely say his name because I choose not to see him. My step dad is in every meaningful way my dad. It means he chose to be a part of my life.
There are either some major unresolved issues that you should either address, or seek therapy for, or you are leaving a lot out.
And if there are issues you haven't addressed, get them resolved before adding pregnancy and a newborn to this situation. They make everything harder, stress every weak spot in a relationship.
You are definitely being extremely unreasonable.