HELP- Invite Question!

Hi all, question about engagement party. My FI and I decided to only invite immediate family and bridal party to the e-party. Now when I asked my FI to get a list from his brother of who to invite...his SIL put her own parents on the list. My FI said just to invite them...but I dont think its right, They arent family to my FI or I. My friends and Mom dont think I should invite them. What do you think?
TIA
Stephanie
11*4*06