I’m not calling back

Some 3 weeks ago we called our families and told them we’re pregnant again. Except my SIL, we’re not on good terms. In past 2 days my SIL’s husband has been calling me. Perhaps someone told them. I don’t have their number saved so at first I didn’t recognize it. I really don’t care to call them back or pick up, pretend and talk about my pregnancy to them. I think it should actually be my SIL calling her brother. The next time we’ll probably see them is for Xmas at my in-laws. Would you call back? Should I care?