Not sure how to act

So my husband and I got pregnant unexpectedly. We were over the moon excited but we hadn’t been trying at all. My sister-in-law and her husband have been trying for almost three years with no luck. I felt so guilty about telling them we were pregnant. I know we didn’t do anything wrong and neither of them were angry or rude about it. She posts a lot of things about how she’s going to be “one of those cat moms” or says things like “if I ever get to have a baby” and kind of laughs it off. It honestly breaks my heart. I know it’s hard for them and I feel so bad. I just never know what to say or do in those situations. I want them to have a baby so bad. I just wish it happen for them.