Parenting (step parents) advice

(Sorry it’s a long post, but please any help would be appreciated)

Me and my current bf have been together close to 2 years and we are expecting a daughter (Due date 10.28.18 so excited!!😁) anywho lol I have a daughter from a previous relationship (she’s 7). Her father is very present in her life. He keeps her every other weekend and has visitation a couple times a week for a few hours after school. So a very active part of her life. My current bf says that since he’s in the picture and we will be raising BOTH children together that he should be able to punish my older daughter as well as needed. That he should be included in that part of the parenting. I’m conflicted, I see his point but Idk how her father will feel about it and while we coparent well, we don’t get along well so we don’t talk much. So if anyone has advice about this I’d love it hear it. Is it normal for stepparents to be apart of the disciplining or should I handle it?