I'm in my boyfriend's sister's will?!?! um... help?

Gracie
Totally random but I just found this out last night. 
So my bf and I aren't officially dating and won't be until after I graduate, next summer. Well my mom and his went to the salon and we're talking. Apparently his older sister was writing her will and put him and I down to take her kids if anything happens to them😳 I'm 17 and just realized how huge of a responsibility that is!