Annoying SIL and neice

When I announced I was pregnant everyone was happy expect for them. They had attitudes the rest of the night and my niece threw a tantrum. She wants to remain the only girl. She’s a very selfish bratty little girl and acts just like her equally as bratty mother. I didn’t care what they wanted, I was wishing for a baby girl and the entire time before I found out what I was having they kept saying “she’s having a boy anyways, she’s having a boy” in a very snarky way to lower my hopes at having a girl since I have two boys already. Well I’m having my third boy and I just know they’re grinning ear to ear about it. It’s just so petty and childish and I expect the childness from the actual child but the grown mother?