Need advice about telling my partners family.

My parter has 3 older sisters. The eldest has one son and has struggled for 5 years to have another and now they’ve decided to do IVF. the middle has no kids and about a year ago decided to do ivf ( to my knowledge they haven’t started ) And the youngest has had 2 kids and due to medical reasons can’t have any more.

We don’t know how to tell the older two sister that were expecting.

We want to be kind and respectful and don’t want to rub it in in any way ...