Obligated to buy gifts

I had my first in July and I obviously want to make it a special Christmas for her. Well my sis told me I need make sure I get her kids some gifts as well like what excuse me I did plan on getting them jammies and undies but she wants me to get games for they switch and I can’t do that because not only is it Christmas but my husband birthday is the 26 and mine is the 28 so if I buy her kids expensive games I’ll be broke but I don’t wanna break the kids heart 🤷‍♀️ so I told her no I can’t do that and she basically said well tell your niece and nephew that 🙄