Pregnant bridesmaids

I have 4 adult bridesmaids, two are pregnant and due in July and august, a third has told us this morning she’s pregnant and due 12 days before our wedding. We are absolutely thrilled for her but worried she might miss the wedding (she’s my future sister in law so we would obviously be disappointed and miss her there even though so excited for a new niece or nephew). I’d actually asked her to be a bridesmaid and we ordered dresses, they’re £250 each and she is a very small size. I need to have a chat with her about what she thinks we should do but has anyone had any joy cancelling an order and getting any money back? We are of course having all the newborns at the wedding (4 in total that we know of), but no other children besides our own.