What should I do

Me and my bf been together 1 year I haven’t met his daughter yet because I am the first person he’s dated since his bm so he doesn’t know how that goes . He has a 2 year old I have a 4 year old . We just found out we’re expecting so I asked if the kids could sit on the stairs holding an ultrasound then when the baby comes they will sit in the same spot holding the baby . He says he doesn’t want to deal with his bm mouth about having his daughter around me . I try to stay out they business I don’t really know if she even knows about me . I’m really emotional and don’t know what to do . I really wanted the pictures done that way but I guess there’s time for him to change his mind .