Hey ladies

Saturday is my sons birthday party and my boyfriend has 2 other kids from a previous relationship. They go with their mothers on saturday-sunday y

She takes them fri night until saturday night. And she's trying to not take them  Well my father in law texted me asking if kids were gonna be at party i go no its their mothers only day with them we were gonna have a party for the kids on sunday so its like they didn't miss it well he responds "well im grabbing the kids they are coming get over it "... like who are u to tell me? A yr or 2 ago he wouldn't let me go to my stepsons party cause we got into a arguement and my bf didnt let me either so i wanna pull the same card since he thinks he has a say

advice??